The National Oceanic and Atmospheric Administration (NOAA) Oceanic and Atmospheric Research (OAR) Laboratories in Colorado and their Cooperative Institute partners are building and deploying four fixed and two mobile fire weather observatories in the intermountain region of the Western United States. The fixed observatories will each have a 449-MHz radar wind profiler; an infrared spectrometer for temperature and humidity profiling; a dual-polarized laser ceilometer; surface radiation and cloud measurements; fast-response wind, temperature, and moisture probes measuring the surface turbulent fluxes of heat, water vapor, and momentum; standard surface meteorology sensors; soil probes measuring temperature and moisture profiles in the ground, and trace gas/aerosol concentration measurements including PM2.5 and PM10 particulate matter concentrations. Two mobile observing units will be created, with instrumentation mounted or transported in a trailer pulled by a pickup truck. These mobile units will be modeled after the Collaborative Lower Atmosphere Mobile Profiling System (CLAMPS) trailers built and operated by the NOAA/OAR National Severe Storms Laboratory (NSSL), but with slightly different instrumentation. Since NSSL has CLAMPS-1 and CLAMPS-2, these mobile units will be referred to as CLAMPS-3 and CLAMPS-4. These newer CLAMPS units will each contain a scanning Doppler lidar in place of the radar wind profiler and the other same or similar but compacted instrumentation deployed at the fixed sites. The instruments will be operated by a diesel generator, unless line power is readily available. Specially instrumented drone aircraft will be deployed along with the mobile observatories. The fixed observatories will be dispersed through the Intermountain West at four sites, each with its own topographical and ground cover characteristics. The mobile units will be stationed at Table Mountain, near Boulder, Colorado, and will deployed to controlled burn and/or actual wildfire events. These fire weather observatories will give researchers detailed surface and boundary-layer measurements to gain a better understanding of fire weather behavior. Some of the data and products from the observatories will be shared with weather forecasters, incident meteorologists, and other end users in near real time.

 

Characterizing global circulation in the MLT is an ongoing scientific endeavour, which can be challenging due to the scarcity of global observations. Remote sensing techniques by meteor radar and Doppler Rayleigh lidar offer two of the most accurate ways to measure the key dynamic variables, wind and temperature, in the middle atmosphere. Meteor radars can operate over the altitude range of approx. 70 to 110 km depending on system specifications, while Doppler Rayleigh lidar can retrieve winds from 25 to 90 km, depending on system specifications and sky clarity. We present a comparison of mean winds measured in the overlap region between approx. 70 to 90 km at Kühlungsborn (54N, 12E) and ALOMAR (69N, 16E). This work represents the first extensive comparison covering more than 2 years of horizontal winds in the upper mesosphere between co-located lidar and radar. We will present a climatology as well as a few illustrative case studies.

A DIfferential Absorption Lidar (DIAL) has been developed at National Atmospheric Research Laboratory, Gadanki (13N, 79E), India for measurement of ozone concentrations to understand Upper Troposphere & Lower Stratosphere (UTLS) exchange processes and stratospheric ozone changes. The system measures ozone concentrations in the height regions of 10-35km. The system is designed and developed taking ozone absorption cross-section in these regions into consideration. Accordingly, ON-OFF wavelength pair of 308 and 355 nm is chosen for Stratospheric ozone concentration measurements. The ON wavelength is generated by Excimer laser filled with XeCl, Helium, compressed Air and OFF wavelength is generated by third harmonic of Nd:YAG laser i.e 355nm. The backscattered returns from the two wavelengths are collected alternately by Newtonian feed telescopes with 50cm aperture each in multiple receiver concept. The signals from the telescopes are fed to the detector through an optical fiber bundle. The signal is then given to a data acquisition unit with analog and photon counting features. The analog and photon counting modes are chosen to give a high dynamic range to the system, from high intensity signal at lower altitudes to low intensity signals from higher altitudes. The analog signal is acquired at 16 bit resolution with sampling rate of 20MSPS. With Photon counting, maximum count rate of 250 MHz is achieved with temporal resolution of 25ns. The ozone concentration profile is obtained by standard methods from the ratio of returns in ON and OFF wavelengths and ozone absorption cross section. The DIAL system is a self calibrated system. The ozone concentration obtained from DIAL system are compared with monthly mean ozone concentrations measured by ozonesondes. They show good agreement with each other in the height regions of 10-30km.

The Buckland Park Stratospheric Tropospheric (BPST) wind profiing radar has been used in various satellite detection experiments and campaigns, which are well reported in the literature [e.g. 1, 2 & 3]. ATRAD in conjunction with Defence Science Technology (DST) group, have operationalised this research and can now routinely detect LEO satellites which transit the BPST beam.

 

Our analysis calculates the (aliased) range, (aliased) Doppler, acceleration, azimuth and elevation of detections. For known RSO’s (resident space objects) these parameters can be compared to those obtained from North American Aerospace Defense Command (NORAD) two line ephemeris (TLE) data, which is forwards propagated in time using a simplified perturbations model. Non-catalogued objects are arguably more important information to Defence, and we will show examples of such detections.

 

A major aim of this work is to simultaneously detect ST winds and satellites, thus enabling all wind profiling radars to play a role in space domain awareness while maintaining their primary purpose. We will present results of operational detections, in conjunction with ST winds from the BPST. We will discuss the advantages and challenges of multi-purpose radar, and consider the future role these class of radars will play in Australia.

 

References

 

[1] Holdsworth, David A., Spargo, Andrew J., Reid, Iain M. and Adami, Chris, (2020a), Low Earth Orbit object observations using the Buckland Park VHF radar, Radio Sci., 55, e2019RS006873, https://doi.org/10.1029/2019RS006873

 

[2] Heading, E., S. T. Nguyen, D. Holdsworth, I.M. Reid, Micro-Doppler Signature Analysis for Space Domain Awareness using VHF radar, Remote Sens. 2024, 16, 1354. https://doi.org/10.3390/rs16081354

 

[3] Holdsworth, D.A.; Spargo, A.J.; Reid, I.M.; Adami, C.L. Space Domain Awareness Observations Using the Buckland Park VHF Radar. Remote Sens. 2024, 16, 1252. https://doi.org/10.3390/rs16071252

 

The Algorithm for Head Echo Automatic Detection (AHEAD) represents a breakthrough in meteor detection technology. Engineered with high sensitivity and a multitude of variables in mind, AHEAD adeptly discerns meteor head echoes, even when fragmented into multiple segments, ensuring they are accurately identified as singular echoes. With AHEAD, we can now capture the intricate characteristics of meteor head echoes in their entirety, providing a deeper understanding of these phenomena.

 

To delve even further into the study of head echoes, we harnessed the power of a specially trained Sequence-to-One Regression convolutional neural network. This advanced tool allowed us to categorize echoes into six distinct types, each revealing unique signal patterns and behaviors within radar systems. Type I echoes, the most common, exhibit a low signal-to-noise ratio and lack distinct features, constituting approximately 75% of all detections. In contrast, Type II echoes demonstrate sudden power changes within a 0.4-microsecond Inter-Pulse Period, equivalent to 60 km. Type III echoes, considered as 'good' meteors, consistently align with the radar beam pattern and display a smooth bell curve. Types IV and V echoes are characterized by strong, irregular, and regular interference patterns, respectively. Finally, Type VI echoes stand out for their remarkable ability to traverse multiple radar lobes.

 

This meticulous categorization significantly amplifies the meteor community's capability to analyze meteoroid entry, atmospheric dynamics, and radar scattering properties. It represents a significant leap forward in the field, offering not only enhanced detection methods but also profound insights into atmospheric science. These findings have the potential to shape future research endeavors and practical applications in meteor research and related disciplines.

The mesosphere and lower thermosphere (MLT) mark the transition zone where the lower atmosphere blends into outer space, subject to significant influences from both terrestrial and extraterrestrial factors. Despite its importance, comprehensive understanding of the MLT dynamics remains limited, primarily due to challenges associated with direct measurement techniques and the complex interactions occurring therein. In this study, we propose a method to uncover the hidden mesoscale dynamics in the MLT by combining sparse observational data with fundamental physical principles. Specifically, we employ meteor radar observations and the Navier-Stokes equations to reconstruct 4D wind fields, aiming to reconcile noisy observations with the underlying physics that govern the dynamics in the MLT. Validation of our methodology involves benchmark analyses using synthetic data and its application to real meteor radar observations in South America, Norway, and Germany. This innovative approach represents a significant advancement in accurately characterizing both linear and non-linear dynamics within the MLT, overcoming existing methodological limitations and providing valuable insights into this atmospheric region's behavior.

Atmospheric gravity waves (GW) couple different layers of the atmosphere by transporting horizontal pseudo-momentum vertically from their excitation to the point where they dissipate. While the GW drag in global circulation models in the stratosphere is increasingly well-represented, their complex interactions and momentum deposition in the mesosphere is inadequately captured. A comparison of models with observations revealed that model winds in the mid to high latitudes even have the wrong sign above approximately 80km. This is due to the insufficient representation and parametrization of GWs and their influence at these mesospheric / lower thermospheric altitudes.

 

To better understand the effect of GWs on the background flow, more observations in the altitude range above 80 km are needed. One form of observation is provided by airglow imagers, which detect, for example, the infrared emission from OH at an altitude of ~86 km. GWs modulate the temperature of the atmosphere at this altitude, which in turn determines among other things the intensity of the detected radiation. Airglow imagers such as the Advanced Mesospheric Temperature Mapper (AMTM) developed by Mike Taylor and Dominique Pautet observe GWs over a horizontal range of approximately 200 km x 200 km throughout the night. Instead of linear monochromatic waves, the observations reveal a chaotic superposition of waves with many different properties.

 

These GW properties such as amplitude, wavelength, and frequency must be measured precisely in order to systematically determine the GW momentum flux. Since GWs occur not only intermittently in localized regions but also can occupy quasi-stationary very large spatial areas and their spectral components are functions of space and time, a mathematical tool is needed that allows for the examination of nonlinear non-stationary signals in multiple dimensions. This tool is provided by the multidimensional continuous wavelet transformation (CWT).

 

Applying the CWT to a 1D dataset, such as a time series, results in a 2D wavelet spectrum that possesses spectral power as a function of time and frequency. Since the AMTM detects wave signatures in two spatial and one time dimension, the result of the CWT is a 6D space. The question arises of how to most effectively explore this multidimensional wavelet spectrum and how to identify individual wave packets. In my approach, I use hierarchical density-based spatial clustering of applications with noise (HDBSCAN). The clusters identified in spectral power are used to derive the spectral properties of individual wave packets and to reconstruct the wave packets themselves.

 

The methodology is first applied to artificial datasets where multiple waves with different properties are superimposed. This allows for the determination of the methodology's constraints. Finally, the methodology is applied to real observations from the AMTM in Río Grande, Argentina.

 

Ultimately, the addition of co-located temperature and wind measurements by a middle atmosphere Rayleigh lidar and a meteor radar in Río Grande, enable a precise determination of GW momentum flux in the mesosphere / lower thermosphere.

 

Time series of mesosphere/lower thermosphere half-hourly winds over Collm (51.3°N, 13.0°E) have been obtained from 1984 – 2008 by low frequency (LF) spaced receiver measurements and from 2004 to date by VHF meteor radar Doppler wind observations in the height range 82 – 97 km. These observations are analysed with respect to mean winds, tidal amplitudes, and gravity wave (GW) climatology and trends. Mean winds and tidal amplitudes and phases are obtained from least-squares fitting on half-hourly mean horizontal winds. From half-hourly differences of zonal and meridional winds, GW variance proxies have been calculated that describe amplitude variations in the period range 1 – 3 hours. After applying corrections to account for instrumental differences, GW climatology and time series have been obtained. The mean GW activity in the upper mesosphere shows maximum amplitudes in summer, while in the lower thermosphere GWs maximize in winter. At altitudes around 90 km, positive/negative long-term trends are visible in winter/summer. In the lower thermosphere, however, long-term amplitude trends are generally positive. Qualitative agreement with satellite observations is visible. These trends are compared with long-term trends of mean winds, which generally show increasing zonal wind trends, but meridional winds decreasing with time. Quasi-decadal variations of GW amplitudes and mean winds are also visible, showing a possible influence of the 11-year solar cycle. Interannual wind, tidal amplitude, and GW variations show a possible influence of lower atmosphere circulation patterns like ENSO.

 

Planetary waves (PWs) and tides are prevalent phenomena in the mesosphere and lower thermosphere, yet their study has been hindered by limited data availability. Previous approaches have predominantly relied on single-station and -satellite analysis methods, which lack the capability to adequately discern temporal and horizontal scales. To address this challenge, we developed the phase difference technique (PDT), a two-station method. Unlike conventional analyses, PDT leverages intercontinental spectral coherence to estimate the zonal wavenumber of underlying waves. This innovative approach enables the discrimination of normal modes (NMs) from other PWs, facilitates the differentiation between migrating and non-migrating tides, and offers insights into wave-wave nonlinear interactions within spatial constraints. Application of PDT across various two-station configurations of meteor radars from multipole longitudinal sectors has unveiled numerous phenomena, including the discovery of 4.8- and 4-hour migrating tides and various nonlinear interactions between PWs and tides, notably the PW second harmonic generation. Furthermore, our analyses have unveiled statistical characteristics of planetary-scale waves and tides, including their responses to seasonal changes and sudden stratospheric warming events (SSWs). Notably, multi-day oscillations are predominantly governed by PW NMs, exhibiting a distinctive seasonal pattern characterized by specific period/wavenumber dynamics during the summer half-year and a notable association with SSWs during winter. While the relationship between PWs and SSWs remains a subject of active debate, our study significantly contributes to clarifying this discourse.

Mean winds play an important role in several atmospheric processes in the middle and upper atmospheres. They have a significant impact in tropical regions, influencing different atmospheric waves that carry momentum and energy from the lower atmosphere to these altitudes. Thus, understanding and monitoring them is an important task. However, no single technique is available to measure them, covering the complete middle and upper atmospheres. Therefore, an attempt has been made to obtain mean winds over a tropical region, Tirupati/Gadanki (13.5oN, 79.2oE), by combining reanalysis, ground-based, and satellite-based datasets. A combined dataset from ERA5 reanalysis data from the surface to 80 km, SVU Meteor radar (Tirupati) data in the altitude range of 70 to 110 km, and NASA ICON (MIGHTI) satellite data from 90 to 300 km is used to obtain mean winds covering the complete middle and upper atmosphere. Before combining, they are thoroughly validated using simultaneous independent measurements (Radiosonde, MST radar) in the overlapping regions. Very good agreement between ERA5 reanalysis and radiosonde measurements is observed between the surface and 35 km. Similar good agreement is also found between meteor radar and ICON/MIGHTI in the overlapping region of 90-110 km, which made us combine to investigate mean wind variability (diurnal, monthly, and seasonal) covering the complete middle and upper atmosphere. Strong diurnal variability in the thermospheric (150-300 km) zonal winds is observed, reaching maximum westward (eastward) winds as high as 120 m/s (80 m/s) irrespective of the seasons. Large diurnal variability in meteor winds with strong westward winds at around 100 km is observed at noon and gradually changing to eastwards at midnight. The meteor mean winds were observed to have westward winds during the equinoxes and eastward winds during the solstice. In the thermosphere, at all altitudes, winds are westward during daytime and eastward during nighttime, with enhanced westward winds during summer. Tidal (diurnal and semi-diurnal) variability is further obtained for the first time, covering the complete middle and upper atmosphere. The details of the variability in different tidal amplitudes from the surface to the thermosphere will be presented.

The characteristics of mean winds and meteor echoes in the Mesosphere and Lower Thermosphere (MLT) region are investigated using eleven years (2013-2024) of data from an advanced meteor radar installed at Tirupathi (13.63°N, 79.4°E), India. Maximum meteor echoes appeared around 90 km, and a strong diurnal variation in meteor echoes is observed, with the maximum (minimum) during early morning (peak daytime) hours. An increase in meteor count by 5-26% during meteor shower events is noticed, with the highest occurring during the Geminids, followed by the Quadrantids and Aquarids meteor showers. In general, a decreasing trend in meteor count is observed over the last 11 years. However, a clear signature of solar cycle influence on meteor counts is noticed, with peaks (lows) during solar maximum (minimum) years. Slight seasonal variation in the maximum meteor count at peak altitude is noted, with the highest during NH Summer, followed by Fall equinox, NH winter, and the minimum during the spring equinox. Meteor peak altitude shows a slight increasing trend (100 m) over the last 11 years.

 

A strong variation (~60 m/s) in the seasonal mean diurnal variation is observed, suggesting the effect of tides in the MLT region. Background mean zonal winds show a clear semi-annual oscillation in the mesosphere (MSAO), with a peak amplitude of 20 m/s at 80 km, whereas meridional winds are characterized by an annual oscillation as expected. Weak magnitudes in MSAO are observed during the disturbed stratospheric quasi-biannual oscillation (SQBO) in 2015 and 2020-2021. Interestingly, these years also coincide with the strongest cold and warm phases of ENSO, respectively, suggesting the role of lower atmospheric processes in the middle atmospheric structure and dynamics. Long-term trends in mean winds constructed using Rocket, Satellite (HRDI), MST radar, and Meteor radar data during 1971-2024 in the overlapping regions are also presented and discussed in relation to anthropogenic influences on middle atmospheric structure and dynamics in a changing climate.

 

Around the March equinox of 2023, meteor radars observed extreme mesospheric westward winds that were seen globally, but confined to low latitudes. These strong winds took place during the first phase of the Mesospheric Semiannual Oscillation (MSAO), which was the strongest of the last decade (2014-2023). The westward winds reached -80 m/s at 82 km of altitude in late March and decreased with increasing altitude and latitude. The Whole Atmosphere Community Climate Model with thermosphere-ionosphere eXtension constrained to meteorological reanalysis up to ~50 km does not capture the observed low-latitude March Equinox behavior. In this work, we will present an analysis at mesoscale and planetary scales over the South American sector and the Asian sector and discuss the role of mesoscale gravity waves and migrating diurnal tides as the main drivers of these strong winds.

 

Tides and planetary waves (PWs) have a large impact on the dynamics of the mesosphere and lower thermosphere (MLT). Depending on the seasons and background wind conditions, the amplitude and propagation characteristics of tides and PWs are modified. The seasonal variation of tides and PW characteristics are explored to some good extent. However, the inter-annual variations of tides and PWs during the summer and fall-to-winter transitions along with their impact on the background atmospheric dynamics are not understood well.

 

To understand the role of neutral dynamics on the October effect seen in very low frequency (VLF) observations, we have studied the interannual variation of tides (particularly semi-diurnal-S2) and PWs amplitude during the summer and fall transition period at the high and middle latitudes. To estimate the tidal and PW amplitudes, we used 1 hour (1 km) temporal (vertical) resolution Saura and Juliusruh partial reflection radar (PRR) zonal and meridional winds at high and mid-latitudes, respectively. To extract the tidal and PW amplitudes, we applied a fast Fourier transform of 42 days window with 1 hour sliding. This analysis has been carried out for the altitude range between 75 and 90 km for Saura and Juliusruh radar winds from the year 2005 to 2023. To investigate the interannual variations, we looked into the maximum and minimum amplitudes during the summer and fall-to-winter transition periods. Furthermore, we also looked into the zonal wind reversal from summer to fall/winter. We found that the VLF October effect is more connected to the reversal in the zonal wind than the S2 amplitude minima both in the high and mid-latitudes. The day of the S2 maximum and VLF October effect coincide during the high and moderate solar activity years, however, during the low solar activity condition the S2 maximum was observed earlier than the VLF October effect. Detailed results and physical reasoning will be presented in this presentation.

 

The Mesosphere Lower Thermosphere (MLT) region is highly dynamic, influenced by atmospheric waves and their associated momentum deposition. Among the different atmospheric waves, the Quasi 2-day wave (QTDW) stands out as a significant contributor to the MLT dynamics. This study examines QTDW characteristics over a low latitude station, utilizing three years of data (November 2013 to October 2016) from the meteor radar at Sri Venkateswara University, Tirupati, India. Daily QTDW amplitude and phase were extracted from the hourly zonal and meridional winds and fractional ambipolar diffusion using a least square fit. The study discusses the composite, seasonal and interannual variations of QTDW in detail. The results showed clear seasonal variability in QTDW activity with enhanced activity during the late solstices (January/February and July/August months) and weak enhancement during the month of October in horizontal winds. Fractional ambipolar diffusion shows strong activity during equinoxes, followed by the summer solstice. To quantify the impact of QTDW on the mean winds, QTDW momentum flux ((u^' v^' ) ̅,(u^' w^' ) ̅,(v^' w^' ) ̅) has been estimated using the horizontal winds and meteor decay time, which is proxy for temperature. The momentum fluxes showed a clear seasonal variation and height variations. This study is the first of its kind to quantify the horizontal and vertical momentum fluxes of QTDW over a low-latitude MLT region.

The Rayleigh Lidar system with improved laser power is in continuous operational mode on all cloud free nights since mid-January 2007 installed at National Atmospheric Research Laboratory (NARL), Department of Space, Gadanki (13.5°N, 79.2°E), India. From this lidar, the vertical temperature profiles are derived using the method given by Hauchecorne and Chanin [1980]. The lidar temperature observations over Gadanki show a few mesospheric inversion layer (MIL) events during 20–25 January 2007. The MIL amplitudes in SABER temperatures averaged for 10°N–15°N and 70°E–90°E show a clear 2- day wave modulation during 20–28 January 2007. The wave gets largely suppressed during 20–26 January 2007 as the condition for vertical propagation is not favourable, though it prevails at lower heights. The two-dimensional spectrum of lidar temperature observations available for the nights of 20, 22, and 24 January 2007 shows the presence of gravity wave activity with periods of 18 min, 38 min, 38 min, and vertical wavelengths of 6.4 km, 4.0 km, 6.4 km respectively. The present study shows that, the mesospheric temperature inversion is caused mainly due to the gravity wave breaking and the inversion amplitude may get modulated by the interaction between gravity waves and planetary waves. The eddy diffusion associated with gravity wave drag may also cause suppression in the planetary wave activity.

 

The presence of quasi 6- and 10-day oscillations in neutral atmosphere dynamics have been registered during August-September 2019, when an unusual sudden stratospheric warming (SSW) has been observed in the Southern Hemisphere. In this work, we have used the meteor winds observed over São João do Cariri (7.4°S, 36.5°W) and Cachoeira Paulista (22.7°S, 45.0°W) at Brazil, as well as over Wuhan (30.5°N, 114.6°E) and Mohe (53.5°N, 122.3°E) at China, to investigate the presence of quasi 6- and 10-day oscillations in the upper mesosphere and lower thermosphere (MLT) region. The 6-day oscillations have occurred after the Antarctic SSW at 7.4°S and 22.7°S, whilst at 30.5°N this oscillation appear from mid August to September and at 53.5°N during September. Presence of the quasi 10-day oscillations have been observed during September at 7.4°S, 22.7°S and 53.5°N, and during August at 30.5°N. Amplitudes of the 10-day wave observed over 7°S reaches values that exceed those for other 3 sites. Aspects about the presence of these oscillations in the MLT region at Southern tropical and Northern middle latitude, during this distinct SSW event will be discussed.

 

Symmetric and antisymmetric parts of the solar migrating semidiurnal tide (SW2) in the mesosphere and lower thermosphere are examined using 21 years of temperature measurements by the SABER instrument onboard the TIMED satellite. It is shown that symmetric and antisymmetric parts of SW2 are comparable in amplitude, but their spatiotemporal characteristics are different. Amplification is observed in the antisymmetric part during the major sudden stratospheric warmings (SSWs) in January 2006, 2009, 2013 and 2019. Comparisons with models will be presented and possible causes will be discussed.

 

A fundamental problem in plasma turbulence is understanding how energy cascades across multiple scales. In this presentation, a new weak turbulence theory is developed to explain how energy can be transferred from Langmuir or Upper-Hybrid waves (~10 MHz frequencies and 20-cm wavelengths) to ion-acoustic waves (~kHz frequencies at 3-meter wavelengths). A kinetic approach is used where the Boltzmann equation is Fourier-Laplace transformed, and the nonlinear term is retained. A unique feature of this approach is the ability to calculate power spectra at low frequencies, for any wavelength or magnetic aspect angle. The results of this theory explain how the predominant type of 150-km radar echoes are generated in the ionosphere. 150-km echoes are strong, coherent backscatter observed by equatorial radars since the 1960’s, however their generation mechanism has been unknown until now. It is shown that the generation process first relies on peaks in the suprathermal electron velocity distribution to drive a bump-on-tail like instability that excites the Upper-Hybrid mode. This excited wave then couples nonlinearly to the ion-acoustic mode, generating the ~10 dB enhancement observed by radars. This theory also explains why higher frequency radars like ALTAIR do not observe these echoes.

Radar backscattered echoes from the mesosphere and lower thermosphere occur in discrete height regions in the form of layers with occasional quasi-periodic signal intensity variations. Among these, echoes coming from the daytime mesosphere and valley region (the region in between the E and F regions) continue to be of scientific interest to the radar atmospheric researchers since their origins have not yet been fully understood. The radar echoes from mesosphere are believed to be due to electron density fluctuations linked with neutral turbulence. The generation/sustenance of neutral turbulence at meter scale (responsible for VHF backscatter), however, is intriguing since they are supposed to be damped by viscosity in that height region. On the other hand, in the valley region, occurrence of the 150-km echoes show diverse characteristics, which could not be accounted for by the concurrent theories. This paper aims to present a comprehensive picture on the radar observations of mesospheric and 150-km echoes, including their frequency dependence, layered properties and dynamics, based on extensive observations made from Gadanki and the recent progress made in understanding these two echoing phenomena.

 

In this work, we present daytime vertical plasma drift models for the Indian and Indonesian sectors. We use vertical plasma drifts estimated using the Doppler shifts of 150 km echoes observed by the 53 MHz MST radar, Gadanki, India and 47 MHz Equatorial Atmosphere Radar (EAR), Kototabang, Indonesia. Notably, the estimated vertical plasma drifts at the two locations agree exceedingly well with those measured by the CINDI onboard C/NOFS. The models have been developed using feed forward artificial neural network. The model produces vertical plasma drift as a function of local time and day-of-the-year, providing local time, day-to-day, and seasonal variations in vertical plasma drift with maximum error of ~2.7 m s-1. The model successfully reproduces the local time and day-to-day variations in vertical plasma drifts, which are unique aspects of these models. Importantly, we show that while the plasma drifts at the two locations in general agree with each other, on many days they differ remarkably despite that these locations are longitudinally separated by only 20°. The local time variations in the vertical plasma drift provide unique opportunity to study electrodynamics and ionospheric weather, which cannot be done using satellite-based models. Also we find that the model drifts differ remarkably from those of Scherliess-Fejer (1999) model, which is so commonly used by the ionospheric community. The results and usefulness of the models are presented and discussed.

 

Sanya Incoherent Scatter Radar (SYISR) and its tristatic system is the newly build ISR in low latitude China. In this presentation, we will generally describe its development process. Then we will highlight some interesting measurements made by SYISR, including the 150 km echo enhancements, dynamic sporadic E layers, day-to-day variability of low latitude neutral winds and electric fields.

Previous studies suggest that the planetary waves in mesosphere and low thermosphere could modulate the occurrence of equatorial plasma bubbles (EPBs) via altering post-sunset F layer height. Using simultaneous observations by GNSS receiver networks, two equatorial ionosondes separated by about 10° in longitude, HF and VHF radars, we investigated the day-to-day variations of post-sunset F layer height and EPB occurrence in southeast Asia during the quasi two-day planetary wave (QTDW) event in July 2023. The results showed that the post-sunset F layer height over Bac Lieu (9.3°N, 105.7°E) and EPB occurrence had a quasi two-day variation. However, such a two-day variation of F layer height was confined in a very limited longitude, that is contradictory to the planetary scale characteristics of QTDW. We suggest that the quasi two-day variations of post-sunset F layer height and EPB occurrence over a specific location were not necessarily due to the QTDW in mesosphere and low thermosphere. The local seeding source, as characterized by satellite traces in ionosonde ionograms, could drive the small-scale longitudinal structure of F layer height and play an important role in shaping the quasi two-day variation of EPB. The results implicate that the connection between planetary waves and the EPB occurrence over a specific location should be interpreted carefully, even if the day-to-day variation of post-sunset F layer height shows periodic behavior with planetary wave scale.

Incoherent scatter spectrum observations have been conducted with the AMISR-14 radar system pointing at different magnetic aspect angles around the perpendicular to the geomagnetic field (B) direction. The AMISR-14 radar operates at a frequency of 445 MHz and is located at the Jicamarca Radio Observatory (Lima, Peru) in the magnetic equatorial region. As expected, the incoherent scatter measurements exhibit dependence on the magnetic aspect angle. In the perpendicular to B direction, the spectrum is narrow and sharp. It also shows sidebands at the lower hybrid resonance frequency. One degree from this direction, the spectrum has become smoother with a shape similar to a Gaussian function. At greater angles, the spectrum exhibits the typical double-hump shape for incoherent scatter observations away from the perpendicular to B direction. In this work, we are modeling the magnetic aspect angle dependence of the observations using the general framework of the incoherent scatter theory accounting for the effects of Coulomb collisions. These effects are modeled using a Fokker-Planck collision model with constant friction and diffusion coefficients. Using off-perpendicular to B spectral measurements, we can typically measure electron and ion ionospheric temperatures. In our case, the aspect angle dependence of our spectral observations allows us to estimate other ionospheric parameters. For instance, by adding the perpendicular to B observations, we can also estimate magnetic field intensity from the lower hybrid lines and collision rates from the width of the spectrum. We will describe the details of our model and present our preliminary results in estimating ionospheric parameters as a function of range.

Metal species like Fe, Mg, Na, and Ca⁺ in the space-atmosphere interaction region (SAIR) come from cosmic dust when burning as meteors in the upper atmosphere. These metal species form their main layers about 75 to 105 km in altitudes, providing excellent tracers for resonance-fluorescence lidars to profile temperatures and winds and to study various atmospheric waves and fluxes in the mesosphere and lower thermosphere (MLT). Since 2011 with lidar discoveries in Antarctica, neutral metal species like Fe and Na have been observed in the thermosphere and ionosphere up to ~200 km, showing gravity or tidal wave signatures. Such thermosphere-ionosphere metal (TIMt) layers are not limited to Antarctica but have been observed nearly all over the world from the polar to mid and low latitudes. Following these studies, Optical Parametric Oscillator (OPO)-based Ca⁺ lidars have detected metal ions Ca⁺ over 300 km in China. In this paper we will present recent results of our studies on the metal layers with high-detection-sensitivity lidars at McMurdo, Antarctica and at Boulder, Colorado. As lidar technologies continue progressing, it is becoming possible that lidars can routinely profile metal layers to ~200 km or higher (in the nighttime only for now) and start to address some topics that are otherwise difficult to address with other observational methods. This iMST16 workshop will provide a good opportunity for collaborations to synthesize lidar measurements with other observations to explore more science issues in the space-atmosphere interactions.

 

Mesospheric icy particles can be observed by lidar and radar. They are known as Noctilucent Clouds (NLC) or Polar Mesospheric Clouds (PMC) and create so-called Polar Summer Mesosphere Summer Echoes (PMSE) when observed by radar. The ice clouds are formed in the summer polar mesopause region when temperatures drop below the frost point. Meridional winds can move these clouds towards mid-latitudes, where the ice particles eventually sublimate because of increasing temperatures. NLC/PMSE are important tracers for middle atmosphere dynamics and temperatures, and, additionally, they are an important target for high-resolution lidar and radar studies. Even if both phenomena are closely related to each other, they differ in some aspects, like, e.g., their sensitivity to the size distribution of the particles. Combined observations by lidar and radar are therefore particularly important. Unfortunately, PMSE observations are typically limited to daylight conditions, but daylight measurements of NLC require special lidar techniques. To the best of our knowledge, our site at Kühlungsborn/Germany (54°N, 12°E) is the only location at mid-latitudes, where simultaneous observations of NLC and PMSE are possible. This enables, e.g., daily studies with low electron densities during twilight, and studies of NLC/PMSE parameters in a region that is only sporadically cold enough to allow ice particles to exist. We will describe the long-term data set of ice clouds in the mid-latitude mesopause region. We will present similarities and differences between our observations of NLC and PMSE and compare them to results from high latitudes. Additionally, we will show the relation between the occurrence of ice clouds and ambient wind conditions as observed by co-located meteor radar and Doppler wind lidar.

In a recent publication, Hocking and Pimmegar (2022) demonstrated the existence of Mid-latitude Mesospheric Summer Echoes (MMSE) as far south as 46.5^oN. The radar frequency used was 45.47 MHz. In this presentation, further searches for MMSE were undertaken at even more southern latitudes; specifically 45.0^oN, 44.4^oN 44.2^oN, and 43.0^oN.

 

Detection of such echoes are important for global climate-change studies altitude, as their detection highlights regions of cold temperatures at ~90 km altitude. Typically the existence of such scattering entities relates to ice-crystals at temperatures below 140K. The importance of choice of frequency is also discussed, and it is emphasized that frequencies less than 30 MHz offer nothing of value in regard to temperatures within the scattering echoes; only detection at frequencies > 30 MHz are valuable in this regard.

 

Observational results of this campaign will be presented and discussed.

 

References

 

Hocking, W.K. and V.L. Pinnegar, "Mid-Latitude Detection of High Schmidt-Number Turbulent Echoes, and Comparison to PMSE and Geomagnetic Variations". Atmosphere, 13, 396, https://doi.org/10.3390/atmos13030396, 2022.

 

http://www.mdpi.com/2073-4433/13/3/396.

 

We present the first results on the mesospheric echoing layers, winds and turbulence observed using a newly established 53 MHz active-phased-array radar system at Haringhata (22.93°N; 88.5°E, magnetic dip angle 36.2°N), Kolkata, India. The radar site is known for deep convection, thunderstorm and lightning activity. The radar is designed to function with a maximum peak-power-aperture product of 3.0×108 Wm2 and is capable of observing the mesospheric echoes. Initial observations show that mesospheric echoes come primarily from altitudes of 65-87 km. Echoes coming from the heights below 80 km are more continuous than their counterpart above 80 km, which are patchy in nature and highly strong at times. Signal-to-noise ratio (SNR) of the echoes are in the range of -15 to 10 dB below 80 km while they are -15 to 15 dB above 80 km. Spectral widths are 2-15 m/s below 80 km and 2-35m/s above 80 km. While SNR generally scales with spectral width, indicating the turbulence as the main driver for generating refractive index fluctuations causing radar echoes, the relationship between SNR and spectral width in the two height regions varies in detail, clearly indicating different underlying sources and dissipation processes of turbulence. The velocity field in the lower region often displays highly organized quasi-period pattern. We have also captured some events showing rich echo structures accompanied with large wind shear, vertical velocity variations, and enhanced turbulence, which suggest the role of Kelvin–Helmholtz instability. The first results obtained using this new radar system are presented, compared with those known from Gadanki MST radar and discussed.

 

The SOUSY Svalbard MST Radar has been in operation in Adventdalen outside Longyerbyen, Svalbard, since 1998. Originally the system was a beam steering system with a five beam pattern, but in resent years the system has only been operated with a single vertical beam and low power, mainly focusing on measuring Polar Mesosphere Summer Echoes (PMSE). In 2019 the radar was upgraded with a new transmitter/receiver system and in 2023 a major overhaul of the antennas, powersplitters and cables has resulted in a much improved signal and removed a lot of clutter from the measurements.

 

During a Solar Energetic Particle event in February 2024 resulting in proton precipitation, we observed Polar Mesosphere Winter Echoes (PMWE) from Svalbard for the first time. This is a record high latitude for the phenomena.

 

This shows the improved capability of the radar after the upgrade, and is promising since we are planning further improvements to the system in the future.

The mesosphere and lower thermosphere (MLT) represents a fascinating region within our atmosphere, serving as the boundary between Earth’s system and outer space. Despite its significance, our grasp of this region’s dynamics remains poorly understood mainly due to the observational challenges it poses. An unexpected observation in the Middle Atmosphere Alomar Radar System (MAARSY) data from July 2016 highlights the complexity of this layer. The data revealed a solitary wave-like event in varicose mode (simultaneous upward and downward drafts) characterized by a spatio-temporally localized nature and remarkably high vertical velocities, exceeding 50 ms^-1. Following this discovery, a comprehensive examination of MAARSY data across seven Polar Mesosphere Summer Echoes (PMSE) seasons, covering the months from May to August between 2015 and 2021, was conducted. This review confirmed that while the varicose mode structure of the 2016 event is not uncommon, instances of extreme vertical velocities that exceed the 3σ threshold are rare, but nonetheless present. Despite having statistically analyzed the frequency and characteristics of these events, their underlying causes remain a mystery. This study seeks to further our understanding of these events by including data from both the Spread spectrum Interferometric Multistatic meteor radar Observing Network (SIMONe) as part of the Multistatic Multi-frequency Agile Radar for Investigations of the Atmosphere (MMARIA) concept in Norway and additional MAARSY observations including multibeam and radar imaging techniques, alongside satellite temperature measurements. By focusing on a selected number of cases characterized by high vertical velocities, we aim to shed light on the ambient conditions under which these unique events occur. This approach not only provides valuable insights into the potential triggers behind these high-velocity events but also represents a significant step forward in understanding the complex dynamics of the middle atmosphere.

This presentation will review the evidence for larger-scale atmospheric gravity wave dynamics that drive instabilities, the instabilities that arise in varying environments, their pathways to atmospheric turbulence, and the turbulence dynamics that account for the downscale cascade within the turbulence inertial range.

The UK MST radar has collected a near-continuous record of wind profiles between 2 and 16 km, from 1997 to 2024, with a time resolution of 30 minutes and vertical resolution 300 m. Observed in these data are patches of spectral broadening due to strong atmospheric turbulence. This study aims at relating the turbulence to underlying dynamical mechanisms in the region 5-15 km, such as wind shear around fronts and jet streams, deep convection, mountain-wave breaking and inertial instability.

 

During a 5-minute measurement cycle, the radar measures 6 vertical dwells and four dwells at 6° off-vertical in four orthogonal azimuths. The raw spectral width of each spectrum was obtained by first subtracting the noise, then identifying the strongest peak and the spectral region around that peak where the signal exceeded the noise, and finally deriving the Gaussian-equivalent width σw from the first and second moments of the identified signal region. Individual dwells from all four 6° beams were averaged over six measurement cycles (33 minutes) to produce a raw spectral width measurement. These raw values were corrected for beam and shear broadening using the methods described by Hocking et al (2016) to give estimates of the broadening due to turbulence. Because the spectral resolution of the radar is 0.154 ms-1, values of corrected spectral width need to be considerably larger than this to be practically useful; for this study a threshold of 0.4 ms-1 was adopted. By the formula presented by Luce et al (2018), based on the MU radar, the turbulent dissipation rate ε ~ σw3/L where L~ 60 m, so 0.4 ms-1 corresponds to ε~10-3 m2s-3, which is strong turbulence (e.g. Ko et al (2019) quote the mean ε for turbulent layers to be 1.84x10-4 and 1.37x10-4 m2s-3 in the troposphere and stratosphere respectively).

 

A preliminary study was conducted for September-October 2016 to establish a method for analysing the turbulence. For each day, image-analysis software (available in IDL) was used to identify and extract turbulent patches meeting the threshold criterion. Erosion and dilatation operations, together with a minimum size (in terms of time-height pixels) was used to retain only the most significant patches. In the resulting set of 221 patches, 217 showed a mean aspect sensitivity (vertical – off-vertical signal power) < 5 dB, consistent with near-isotropic scattering as expected from turbulence. The influence of vertical wind shear on the strength of turbulence was clear from the positive correlation (r=0.62) between the maximum spectral width and maximum shear in the patch. However, mountain waves and convection were also found to be influential in generating turbulence, especially in the troposphere.

 

References:

 

W. K. Hocking et al., 2016. ISBN 978-1-107-14746-1

 

H.-C. Ko et al., 2019. doi: https://doi.org/10.1029/2019JD030287.

 

H. Luce et al, 2018. doi: 10.1186/s40623-018-0979-1

Gravity waves serve as a crucial dynamic coupler between troposphere and stratosphere or even in the upper atmosphere. These waves transport energy and momentum flux in the atmosphere, affecting atmospheric general circulation. In the troposphere, deep convection is the dominant mode of generation of non-stationary gravity waves. Internal gravity waves are a mesoscale phenomenon with horizontal wavelengths ranging from 1 km to several thousand kms and vertical wavelengths ranging from approximately 100 m to a few kms. As a reverse mechanism, these waves also contribute to the initiation of convection and their upscale growth, affecting the organisation of the mesoscale convective systems. Therefore, their high spatiotemporal variability, especially in convective systems, poses significant challenges to their parameterisation. Therefore, examining gravity waves is crucial for better fidelity of numerical weather and climate models.

 

With this overview, over the past decades, MST/ST radars operating at VHF frequencies have emerged as ideal tools for studying these waves due to their optimal vertical and temporal resolution. There have been numerous observational case studies on convectively generated gravity waves over the tropical Indian region using MST radars at Gadanki (13.5^oN, 79.2^oE) and at Indonesia (0.2^oS, 100.3^oE). However, no detailed investigations have been done over the subtropical Himalayan region, where the topography and the convective system can simultaneously affect the generation of gravity waves.

 

In this context, we have utilised the 206.5 MHz ST Radar installed at Nainital (29.4^oN, 79.5^oE;1793m amsl) in the Himalayan foothills to examine the gravity waves generation during deep convective systems induced by western disturbance as well as south-west monsoon. A preliminary analysis during deep convective storms revealed upward propagating gravity waves, usually originating from mid-troposphere travelling into the lower stratosphere region. A combination of spectral and hodograph analysis of zonal, meridional and vertical wind perturbations have been utilised to estimate wave parameters. The interaction of the wave with the highly variable wind leads to the distribution of the intrinsic periods varying from ~34 min – 1100 min and vertical wavelength of ~5.6 – 8.4 km. Furthermore, momentum flux has been estimated to be about 10 times with respect to the pre-convective period and reversing its direction in the Upper Troposphere and the Lower Stratosphere (UTLS) region.

 

This study will offer a comprehensive outlook on the parameterisation of convective gravity waves produced by western disturbances and the monsoon over the Himalayan site. Additionally, it will delve into the mechanisms behind their generation, propagation characteristics, and the budget of momentum flux in the UTLS region. Details will be presented at the upcoming conference.

The PANSY radar is the largest MST radar in the Antarctic and is operated at Syowa Station. Nine years have passed since the PANSY radar became fully operational in October 2015. In this talk, we will show highlights of our study using the PANSY radar. We have shown various characteristics of gravity waves in the troposphere and lower stratosphere including the dominance of gravity waves having near-inertial frequency in all seasons and lower intermittency in the stratosphere than in the troposphere. The dominance of gravity waves having near-inertial frequency is also observed in the upper mesosphere in summer. The vertical flux of zonal momentum associated with gravity waves in the summer mesosphere is mainly positive, which is consistent with previous studies, but in addition, we have shown by analyzing it as a spectrum that the positive momentum flux is mainly due to long-period gravity waves. A beam broadening elimination method, which is applicable to the radars with asymmetrically distributed antennas, was theoretically developed and applied to estimate the broadening of echo spectra due to turbulence. It was shown that the turbulence energy dissipation rate in the troposphere and lower stratosphere changes seasonally, and that the turbulence intensity in the mesosphere increases in winter. It was also found that the turbulence energy dissipation rate weakened when a sudden stratospheric warming (SSW) occurred in the Antarctic in September 2019. Furthermore, in the framework of the international research project, named Interhemispheric Coupling Study by Observations and Modelling (ICSOM), seven international campaigns were conducted in the boreal winters from 2015/16 to 2021/22 by networking the MST radars, meteor radars and MF radars sparsely distributed around the globe. Gravity wave variability during sudden stratospheric warming events and two vortex intensification events were successfully captured. Using initial values from reanalysis data (JAWARA) produced by a newly developed data assimilation system (JAGUAR-DAS), gravity-wave permitting general circulation model simulations were performed for the entire neutral atmosphere up to 110 km. It was shown that the gravity wave modulation in the upper mesosphere by the SSW is not observed over the entire latitude range, but only in the region from the Arctic to lower latitudes in the Southern Hemisphere in the mesosphere. This implies that not only gravity waves but also other waves such as quasi-two-day waves significantly contribute to the interhemispheric coupling between the winter stratosphere and the summer upper mesosphere.

The Beijing MST Radar (39.78°N, 116.95°E) was put into routine operation in late 2011. High-quality horizontal wind, vertical velocity spectral width data, etc., were obtained by improving the power spectral density data processing algorithm. Based on these valuable data sets, new cognition in the aspects of gravity waves and turbulence characteristics in the mid-latitude was obtained. The Inertia-gravity Waves (IGWs) parameters show dependence on both heights, months, and vertical propagating directions, indicating that wave sources are complicated in the area represented by radar observations. Among the plausible candidates for the IGWs wave sources, such as topography, subtropical westerly jet, shear instabilities, etc., vertical shear of horizontal wind was proven to be essential. The turbulence energy dissipation rate ε and the vertical turbulence diffusion coefficient Kz in the troposphere–lower stratosphere over the radar site are revealed. It is found that the seasonal variation of turbulence parameters has noticeable differences at different atmospheric layers. Furthermore, the atmospheric static/dynamic stability and turbulence intensity are the influencing factors of turbulence parameters.

 

The genesis for the Indian Mesosphere-Stratosphere-Troposphere (MST) radar came from the Indian Middle Atmospheric Programme (IMAP) to study the middle atmospheric dynamics and its underlying processes. During the early 1990s VHF radar operating at 53 MHz was set up at Gadanki (13.5N, 79.2E), India, which started operating initially in the stratospheric and tropospheric (ST) mode. It was upgraded to MST mode in 1993. Since then, it has served various scientific experiments not only from India but under international collaboration. Numerous focused campaigns that have national and international importance were conducted. Using this unique data in the last 30 years along with complementary measurements, several stimulating results have been reported covering a wide range of topics covering lower and middle atmospheres including vertical and lateral coupling and long-term trends. The current study will highlight the unique results obtained using long-term observations of Indian MST radar and complementary techniques covering the complete middle atmosphere. Unique results include quantification of the momentum carried by the high-frequency waves generated in the troposphere up to the mesosphere, demarcating the complete tropical tropopause layer using MST radar observations alone, indication for the strengthening of the tropical easterly jet in the recent decade, unusual behavior of the Hadley circulation during drought and El Nino years, the revelation of the mechanisms for the occurrence of mesospheric echoes at the tropical latitudes, quantification of the turbulence, evidence for the role of anthropogenic changes on the dynamics of the mesosphere and generation of the empirical model by combing multi-instrument data sets. These data set also served in validating numerous ground-based and space-borne measurements including several re-analysis products over a tropical latitude. Issues remained unresolved and ways to tackle in future experiments are highlighted.

The seasonal variations in gravity wave (GW) vertical fluxes of zonal momentum, heat, and sodium in the mesopause region are calculated using nearly ten years (from 2012 to 2021) of sodium density, temperature, and wind observations by a narrowband sodium lidar located in Hefei, China (32° N, 117° E). Except in summer, the GW zonal momentum fluxes are mostly westward, with ~80% contributed by the short-period (10 min - 1 h) GWs and anticorrelated with the eastward zonal wind. The mean westward zonal momentum fluxes in spring and winter are -2.55 m²/s² and -1.78 m²/s², respectively, much stronger than -0.98 m²/s² in fall. The momentum flux in summer is primarily eastward, dominated by long-period (1 h-16 h) GWs. These seasonal variations in zonal momentum fluxes are mainly due to the filtering of GWs by the mean background wind at lower altitudes. The annual mean zonal momentum flux is westward at -1.08 m²/s². The calculated acceleration from flux divergence is westward below 93 km, opposite the eastward mean zonal wind. The heat flux below 94 km is downward throughout the year, with no apparent seasonal variation. The annual mean heat flux is primarily downward, with a cooling rate of ~-35 K/day between 87 and 95 km. We will also discuss the seasonal variability of sodium density flux.

Atmospheric gravity waves (GWs) transport their energy and momentum from the lower atmosphere to the upper mesosphere and lower thermosphere (MLT) where these waves reach large amplitudes and dissipate. In this process, they deposit energy and momentum in this region and impart significant forcing to the global atmospheric circulation. GWs are dissipated primarily through convective and dynamic (shear) instabilities when a negative vertical potential temperature or a large vertical shear of horizontal wind is present. The breaking process is often associated with turbulence that leads to energy dissipation and turbulence transport. Observations of instabilities and turbulence are difficult because of their small vertical scales and short durations.

 

We present a detailed analysis of the probabilities of convective and dynamic instabilities in the 85-100 km altitude region based on over 2000 hours of high-quality sodium lidar temperature and horizontal wind measurements made at the Andes Lidar Observatory (ALO) in Cerro Pachón, Chile (30.25S, 70.73W). An important aspect of the analysis is the removal of probability bias caused by measurement errors. On average, probabilities vary from 1-4% for convective and 6-9% for dynamic instabilities in the 85-100 km altitude region. Short-period (<1 hour) waves contribute most to the occurrence of instabilities but the combination of waves at different scales is the most important process that creates instabilities. It is also found that turbulence heat flux is much stronger in unstable regions than in stable regions.

 

Given its complexity to be measured at different spatio-temporal scales, the exploration of the mesosphere and lower thermosphere remains an active area of research. The summer mesopause at middle and high latitudes is the coldest place on Earth, and atmospheric gravity waves are responsible for the emergence of this extreme thermal phenomenon. Although the main physical mechanism behind the latter is understood, a deeper insight into it can be gained from the investigation of the mesoscale energy spectrum.

 

In this work, we have applied velocity filtering techniques to both multistatic specular meteor radar measurements and global circulation model simulations to analyze horizontal wind frequency spectra over southern Patagonia. We decompose the frequency spectra into divergent and rotational parts and find that their energy contributions are equipartitioned at high frequencies. This mesoscale energy equipartition is a feature of stratified turbulence and illustrates the complexity of the mesoscale dynamics in the summer mesopause region.

 

We also analyze the power spectra of observed and simulated mesoscale zonal and meridional winds at middle latitudes in the Southern Hemisphere and show that stratified turbulence (in the statistical sense) plays a role in the mesopause region during summer.

The stratified turbulence (ST) model for the dynamics of the mesosphere-lower thermosphere (MLT) region postulates that for horizontal meso-scales ($\sim$1-400 km), the kinetic energy of horizontal winds dissipates from large to small scales with an approximately mean constant rate. In this investigation, dissipation rates are quantified using meteor-radar observations conducted in Northern Norway. The observed seasonal variability of dissipation rates exhibits maxima during the summer and winter, and minima near the equinoxes, between 80 and 95 km altitude. The results are compared with model predictions and earlier medium frequency radar, rocket, lidar, and satellite observations of MLT turbulence. The findings suggest that multi-static meteor radar measurements of ST can provide a novel way to continuously monitor turbulent dissipation rates in the MLT region.

The presence of noctilucent clouds (NLC) in the mesopause region around 83 km is influenced by temperature and the formation of water vapour from methane in the middle atmosphere. These clouds are sometimes referred to as the "miner's canary" of Global Change at the Edge of Space. Model studies have shown that increases in greenhouse gases, such as methane and carbon dioxide, may be associated with their frequency, intensity, and height over centennial scales. On time scales of seconds to minutes, noctilucent clouds' frozen particles act partially as inert tracers.

 

We showcase the findings from our investigation on the shape, movement, and microphysical characteristics of clouds using lidar, radar, and camera data. To provide insight into their relationship to the background environment, observations will be analysed on time periods ranging from seconds to decades and horizontal scales ranging from a few meters to hundreds of kilometres. The knowledge gained from NLC research is used for studying other phenomena from the lower Stratosphere to the Edge of Space.

Cross-mountain flow over the southern Andes and strong zonal winds extending higher up in the atmosphere allowed for mountain waves to penetrate into the mesosphere on 11/12 September 2019 during the Southern hemisphere Transport, Dynamics, and Chemistry, Gravity Waves (SOUTHTRAC-GW) campaign. The middle atmosphere responses above and in the lee of the mountain ridge were observed by the Airborne Lidar for Middle Atmosphere Research (ALIMA) onboard the German High-Altitude and Long-Range research aircraft (HALO), which provided temperature measurements with both high horizontal (~10 km) and high vertical (1.5 km) resolutions. The observations reveal a complex wave field with multiple superimposed wave packets with horizontal scales ranging from 34 km to 400 km. We employ spectral analysis of observational data and results of numerical modeling to decompose the wave field and analyze the scales and properties of wave packets. Profiles of the vertical flux of horizontal mountain wave momentum reveal contributions of each wave packet to the total momentum flux and gravity wave drag. The derived momentum flux spectrum suggests a peak momentum flux occurring at approximately λ_h = 45 km. Results demonstrate that >80% of the total mountain wave momentum flux is carried by waves with λ_h < 100 km.

Synoptic scale vertical velocities are important to study weather systems and seasonal behavior, e.g., they are considered important in the definition of the mesosphere thermal structure at high latitudes. Their magnitudes are much smaller than the horizontal components, in the order of a few cm/s (after averaging in space or time). These synoptic scale (large scale) values are challenging to measure directly, given their magnitudes and the relatively large variability of the small-scale structures. Meteorologists usually recur to the horizontal divergence to get an estimate of the synoptic vertical velocity in the troposphere. In the lower atmosphere, the observed variability is from a few tens of cm/s to a few m/s. In the mesosphere, the standard deviation in the polar summer mesosphere is around 3-5 m/s. The latter has been obtained by using polar mesospheric summer echoes (PMSE) as tracers. Recently an extreme event has been identified in data from July 16, 2016, showing upward/downward velocities of ~50-60 m/s, i.e., characterized by velocities more than five standard deviations larger than the observed vertical wind variability. This extreme event resembles a solitary wave in a varicose mode, narrow along propagation (3–4 km) and elongated (at least 10 km) transverse to the propagation direction, with a relatively large vertical extent (~13 km). The observations were made using MAARSY with a relatively narrow beam and an aperture synthesis radar configuration on an area of approximately 100 km² around 85 km altitude. Since this observation was not expected and was found serendipitously, a manual search has been conducted in more than six summers of PMSE observations. Various events showing a varicose mode have been observed, but just a fraction of these events is observed with velocities larger than three-sigma but much smaller than the July 2016 event. This event has been recently observed by using a newly developed wind-field analysis that uses physics-informed neural networks (HYPER: HYdrodynamic Point-wise Environment Reconstructor) on multistatic specular meteor radar data covering an area of approximately 40,000 km². The observed extreme vertical velocities with MAARSY and HYPER will be presented and discussed based on statistics and aided by direct numerical simulations.

 

Continuous and reliable measurements of the mesosphere and lower thermosphere (MLT) are key to further the understanding of global atmospheric dynamics. Observations at horizontal scales of a few hundred kilometers (i.e., mesoscales) are particularly important since gravity waves have been recognized as the main drivers of various global phenomena, e.g., the pole-to-pole meridional residual circulation. Multi-static specular meteor radars are well suited to routinely probe the MLT at these scales. One way to accomplish this, is by investigating the momentum flux, horizontal divergence (∇_h∙u) and relative vorticity ((∇×u)_z) estimated from the Doppler shifts measured by the radar network. Furthermore, the ratio between the horizontal divergence and the relative vorticity can be used to determine the relative importance of gravity waves and stratified turbulence. This work will present the first climatology of these estimates, as well as results on the probability distribution of the total momentum flux and the comparison between ∇_h∙u and (∇×u)_z, obtained from almost 10 years of continuous measurements provided by two multi-static specular meteor radar networks: MMARIA Germany, covering an area of more than 250 km radius around (53°N, 13°E), and MMARIA Norway, which covers an area of similar size, but around (69°N, 18°E). Results on planetary-scale dynamics will also be presented to put into context the mesoscale observations.

Vertical air motion plays a crucial role in many meteorological phenomena. It is difficult to measure but VHF Stratosphere-Troposphere radars can potentially provide direct measurements of vertical air velocities in the tropo-stratosphere using various techniques. The 46.5 MHz Middle and Upper atmosphere radar has been operating at the Shigaraki MU Observatory in Japan since 1984. Data are collected every month for about five days or more. For the first time with a ST radar, we present an extended analysis of vertical wind velocity W measurements in the range 2-20 km from 1987 to 2022 (35 years). The W reversal at the height of the jet-stream maximum is detected from measurements performed at vertical incidence almost every month, not only in winter as previously mentioned. Based on an ad hoc theoretical approach proposed by Muschinski (1996), we confirm with an improved model that the (1987-2022) monthly mean profiles above ~4 km altitude can be explained by a contamination caused by a quasi-specular reflection from horizontally advected refractivity surfaces tilted by the horizontal wind shear. The improved model quantifies the observed biases in W, which are consistent with the long-term average levels of power imbalance between symmetric oblique beams. We also established an analytical expression relating between power imbalance, horizontal wind speed and bias in W. This expression also depends on the angular width θs of the scattering diagram of the scatterers. Depending on how θs is independently estimated, the model can be self-sufficient to demonstrate the relevance of the contamination of W by tilted layers. Comparisons with 35-yr averaged profiles of vertical velocities from ERA5 data re-analyses confirm that the radar overestimate W. However, the long-term (35-yr) average W measurements obtained from the combination of symmetrical beams differ significantly from the direct measurements from the vertical beam, suggesting that more investigations are needed.

 

Asian Summer Monsoon Anticyclone (ASMA) develops as a response to diabatic heating associated with convection, encompasses a westerly in mid-latitudes and easterly in the tropics. The occurrence of a Tropical Easterly Jet (TEJ) in the NH summer and Sub-Tropical Jet (STJ) in the NH winter are the prominent features associated with the ASMA region and has a strong influence on the onset and withdrawal of Indian Summer monsoon. Air mass transport within ASMA is one of the major sources of air pollution for the upper troposphere and lower stratosphere (UTLS) region. High amount of water vapour and low amount of ozone are found over ASMA. TEJ and STJ play a key role in the horizontal distribution of tropical upper tropospheric humidity and mid-latitude ozone over the Indian region. The vertical structure of the tropopause layer and its variability at various time scales play an important role in the exchange of minor constituents, especially water vapour and ozone between the stratosphere and troposphere. This exchange process will remove water vapour from the air as it enters the stratosphere and in the reverse direction, intrusion of stratospheric ozone into the troposphere. It has an impact on the global weather-climate system. India has a network of Stratosphere-Troposphere (ST) / Mesosphere-Stratosphere-Troposphere (MST) radars located at Gadanki (13.5oN, 79.2oE, 53 MHz), Cochin (10.04oN, 76.3oE, 205 MHz), Nainital (29.35oN; 79.45oE, 206.5 MHz), Guwahati (26.2oN, 91.75oE; 212 MHz) and Haringhata (22.94oN; 88.51oE, 53 MHz), which are located in and around the ASMA region. In this context, an experimental campaign entitled ‘NetRAD-ASMA (Network of ST/MST radars and balloon borne measurement Campaigns of the Asian Summer Monsoon Anticyclone)’ Phase-I (winter campaign) was conducted during 12-16 February 2024 by operating the network of four ST/MST radars (Haringhata, Gadanki, Nainital and Kochi) along with regular radiosonde (6-12 hrs) measurements from Balasore, Nainital, Gadanki, Silkheda, Pune, Kochi and Trivandrum. In addition, ozonesondes were also launched in an interval of 6 hrs during intense observation period from Balasore and to get background information, ozonesondes were also launched from Gadanki, Trivandrum and Nainital. Micro-pulse, Rayleigh and Mie Lidars were also operated from Gadanki. Initial results shows the enhancement of ozone concentration (Balasore) by about 60 nbar in the lower stratosphere, which persist for about 12-18 hrs. Trajectory analysis shows that the balloon drifted drastically with the upper tropospheric westerlies and thus the stratospheric ozone was measured over the head Bay of Bengal which is about 160 km from the Balasore launching station. Vertical air motion as observed from ST-Radars from the four locations show the presence of strong updrafts and downdrafts. Initial analysis shows that the enhancement of lower stratospheric ozone can be explained in terms of the balance between the photolysis of molecular oxygen and photo-dissociation of ozone as well as adiabatic process in compression and expansion of air mass. The detailed results will be presented and discussed in the upcoming conference.

 

The mesoscale convective system (MCS) is one of the prime causes for the generation of internal gravity waves, which play a vital role in transferring mean horizontal momentum from the lower atmosphere to the middle atmosphere. The vertical convergence of the horizontal momentum flux causes the net acceleration of the large-scale circulation and thermal structure. Thus, it is important to understand how these internal waves affect the middle and upper atmospheric dynamics and quantify their source region in the lower atmosphere. Furthermore, correctly estimating momentum flux associated with these atmospheric waves can help better understand the global mean circulation and thermal structure. However, a detailed investigation of the wind field and its fluctuations, crucial for accurately estimating momentum flux, is often challenging due to the low temporal resolution of conventional radiosonde and aircraft measurements.

 

VHF radars have become indispensable for providing vertical profiles of three-dimensional winds from the surface to the lower stratosphere with high height (~75 m) and temporal resolution (~1 min). In this context, Stratosphere-Troposphere (ST) radar located at Nainital (29.4^oN, 79.5^oE, 1793 m AMSL) in the central Himalayan foothills has been used to estimate the momentum flux during MCS and in normal conditions. We have utilized the modified expression of the coplanar beam method pioneered by Vincent and Reid (1983) to estimate the vertical structure of the horizontal momentum flux components Zonal, u'w' and Meridional, v'w'.

 

u'w'=(v_E'-v_w')/2sinθ [(v_E'+v_W')+(v_N'+v_S')]/4cosθ

 

v'w'=(v_N'-v_S')/2sinθ [(v_E'+v_W')+(v_N'+v_S')]/4cosθ

 

where u'w' and v'w' are the vertical flux of zonal and meridional components of momentum flux, respectively. v_E', v_W', v_N', v_S' are the radial perturbation velocities in the east, west, north and south beams, respectively. The MCS are identified utilizing X-band weather radar and the outgoing longwave radiation obtained from the geostationary satellite. Therefore, a statistical description of the momentum flux estimate will be presented for the MCS. These results are expected to serve as observational evidence for testing the numerical models and their simulation of tracer transport in the UTLS region.

 

Reference

 

Vincent, R.A. Vincent, I.M. Reid (1983), HF doppler measurements of mesospheric gravity wave momentum fluxes. J. Atmos. Sci., 40 (5), 1321-1333

 

Planetary wave (PW) associated dynamical variability in the equatorial and extratropical middle atmosphere during the September 2019 Southern hemisphere minor sudden stratospheric warming (SSW) is investigated utilizing meteor radar wind observations from two southern low-latitude stations and reanalysis data. The analysis reveals a mesospheric warming along with stratospheric cooling at low latitudes. The strong westerly wind at low latitudes decelerates notably near 65 km at the onset of the warming episode, although no wind reversal is observed. The wind spectra reveal a prevalent quasi-16-day wave (Q16DW) before the SSW and a significant burst of a quasi-6-day wave (Q6DW) after the warming event. Possible existence of barotropic/baroclinic instability in the low and mid-latitude middle atmosphere may be responsible for exciting the Q6DW. Both traveling and stationary waves exhibit notable activities during the warming event. Although both zonal wavenumbers 1 and 2 PWs are involved in the event, PW with zonal wavenumber 1 seems to play a vital role in preconditioning the same. Furthermore, the potential vorticity map shows significant latitudinal mixing of airmass between the tropics and high latitudes. The Eliassen-Palm flux diagnosis shows the propagation of the Q6DW and Q16DW from mid to low latitudes during the warming event.

 

Atmospheric tides are global scale oscillations in wind, temperature, density, and pressure. They grow in amplitude in response to decreasing density with height. The tides play vital role in transferring energy and momentum from their source regions to mesosphere and lower thermosphere (MLT). In the present study, the long-term, interannual variability and tendencies of the semidiurnal tide (12-hour) in both zonal and meridional wind components are investigated in the northern polar MLT (~80-100 km) from the meteor radar observations during 1999-2022 over Esrange (67.9°N, 21.1°E). The consistent ability of the radar provided unique long-term dataset of the polar MLT winds from which the tidal amplitudes are derived for the period of about two solar cycles. The tidal amplitudes show some important characteristic features, interannual variability and trends that vary with month and altitudes. In addition, the influence of potential drivers viz., solar activity, Quasi Biennial Oscillation (at 10 hPa and 30 hPa), El Niño-Southern Oscillation, North Atlantic Oscillation, ozone, and carbon dioxide on the variability of tidal amplitudes are investigated from the multiple linear regression analysis. The significant variability and tendencies of the tidal amplitudes can be attributed to the above forcings.

 

Meteor radar wind observations in the mesosphere and lower thermosphere (MLT) from a Southern hemispheric equatorial station are utilized to investigate intraseasonal oscillation (ISO) signature in the period band ~ 20-110 days. The ISO shows conspicuous downward propagation of the peak amplitude indicating the role of the dissipating upward propagating waves for its generation. The eastward propagating waves and tides are surmised to be responsible for communicating the ISO signature from the lower atmosphere to the MLT. The ISO signature shows refraction in the lower stratosphere in course of propagation.

 

Coherent echoes from the equatorial electrojet (EEJ) region was routinely detected at the Jicamarca Radio Observatory (JRO), a facility of Instituto Geofísico del Perú (IGP), using an array of 16 Yagi antennas pointing obliquely to the west with an elevation angle of 35 degrees. The spectra of these observations are composed of two types of echoes (Type I and Type II). Spectral parameters, such as Doppler shift and spectral width, can be independently estimated for each type by a fitting procedure. Due to the asymmetric shape of EEJ Type II spectra, a skew Gaussian distribution had to be proposed to fit the data rather than the usual Gaussian model. It has been demonstrated that the shift of this new approach is the parameter that is a better proxy of the Doppler of the echoes instead of the spectral peak.

 

Ground based techniques can be used to measure zonal winds, such as the ISR technique which is usually performed to estimate zonal wind profiles from measured ion drifts at mid- and high-latitude but cannot be used at low-latitudes due to clutter from coherent echoes at E-layer (EEJ). Additionally, the Spread Spectrum Interferometric Multistatic meteor radar Observing Network (SIMONe) system, deployed in September 2019, can estimate neutral winds from specular meteor trail echoes in the mesosphere and lower thermosphere (MLT) region (70 - 110 km) which includes the EEJ layer, however the time resolution is 1 hour and it probes a larger volume than our oblique radar, then estimated winds will be a result of a contribution from different regions. Space-based missions have also been used to measure these winds such as the Michelson Interferometer for Global High-Resolution Thermospheric Imaging (MIGHTI) on board the ICON satellite, the Wind Imaging Interferometer (WINDII) on the Upper Atmosphere Research Satellite (UARS) among others, but their measurements are not continuous over a specific latitude and longitude as they orbit around the planet. On the other hand, a technique to estimate zonal neutral winds from oblique EEJ type II Doppler shifts, sampled every minute approximately, was proposed by Shume et al. [2005]. This method predicts Doppler shifts from neutral winds, compares the Doppler with the measured ones and updates the winds until the best data-model agreement of the Doppler shift (RMSE < 2.0). Although wind estimations are limited to the EEJ echoes detection and SNR intensity, this method provides high time resolution wind profiles from 97 to 107 km approximately and might be complemented by other techniques. This work presents the first results of neutral wind estimations over IGP-JRO at the EEJ region with a resolution of a few minutes and 700 meters over 10 years of oblique spectra data fitted by a skewed Gaussian distribution.

Interannual oscillations (1<period<10 years) such as Quasi-biennial oscillation (QBO-period of 28-32 months), El-Niño southern oscillations (ENSO- period of 3 to 5 years) originate in the equatorial and low latitude, stratosphere and troposphere, respectively. These oscillations have a large impact on the tropospheric weather pattern as well as the middle atmospheric mean meridional circulations. Their impacts are well reported in the low latitude region. Studies also suggest that these oscillations also have a significant impact on the middle and high-latitude dynamics. For example, the easterly and westerly phases of the QBO affect the polar jets' strength. Recently, studies also reported the QBO and ENSO kinds of periods in the mesospheric winds and phase height measurements over Western Europe. However, along which pathway these oscillations are reaching into the mid-latitude MLT regions is not understood well.

 

In this study, we investigate the characteristics of interannual oscillations using the meteor radar network winds observed over Juliusruh and Collm from 2004 to 2021. Furthermore, we also utilized the WACCM-X winds and temperatures for 40-60°N and 0-20°E latitude and longitude grids. To identify the interannual oscillations we applied the Lomb-Scargle periodogram (LSP) analysis on the monthly and annual mean observation and model simulation data. We found the 2.4 and 3.2-year oscillations in both annual mean zonal and meridional winds, 4.2 and 7-9-year oscillations in the zonal winds, and 5.5-year oscillations in the annual mean meridional winds. To explore the plausible causative mechanism, we segregate the data into four seasons namely, winter (November- February mean), summer (May-August mean), spring (March- April), and fall (September-October), and carried out the LSP analysis. The obtained results and the potential physical mechanism that causes the interannual oscillation in the mid-latitude MLT region will be detailed in this presentation.

 

Significant debate has surrounded understanding the cause of atmospheric variability at scales of minutes to hours. Primary contenders have been (i) gravity (buoyancy) waves and (ii) geostrophic (2D) turbulence. Some arguments have pressed for either (i) or (ii) exclusively, but the truth seems to be somewhere in between, with contributions from both forms of motion being applicable, especially in the troposphere. The relative contributions seem somewhat site-specific. Distinguishing these relative contributions is not trivial.

 

Buhler et al. (2014) have presented one method that is suited to instruments mounted on a sensor moving through the fluid, but it is not well suited to radar applications. In this poster, we present another method which is based on gravity-waves spectra deduced by Fritts and VanZandt, (1987). In particular, the slope of the spectrum at wave periods of a few hours is particularly sensitive to the nature of the underlying cause of the oscillations.

 

Studies have been made at 10 sites in Canada, situated at sites from the poles to mid-latitudes, over a 10-year period of observation. In this poster, results are presented which show that the relative contributions are seasonally- and site-dependent. Further results can be found in Hocking et al., (2021).

 

References

 

Bühler, O., J. Calliesand R. Ferrari,(2014), "Wave-vortex decomposition of one-dimensional ship-track data", J. Fluid Mech, vol. 756,1007-1026.

 

Fritts, D.C. and T. E. VanZandt, (1987), "Effects of Doppler Shifting on the Frequency Spectra of Atmospheric Gravity Waves", J. Geophys. Res., 92(D8), 9723-9732.

 

Hocking, W.K., S. Dempsey, M. C. Wright, P.A. Taylor and F. Fabry, "Studies of Relative Contributions of Internal Gravity Waves and 2-D Turbulence to Tropospheric and Lower Stratospheric Temporal Wind Spectra measured by a Network of VHF Windprofiler Radars using a Decade-long Data-set in Canada", Q. J. R. Meteorol Soc., Vol. 147(740), 3735-3758, https://rmets.onlinelibrary.wiley.com/doi/10.1002/qj.4152, 2021.

Gravity waves (GWs) play a pivotal role in the atmospheric dynamics of Earth. They propagate, break, and dissipate their energies and momenta across atmospheric layers, affecting the atmospheric general circulation. The analysis of wind and temperature fluctuations, observed through lidars and other instruments, provides a means to study the spectral properties of GWs, such as their frequencies, amplitudes, and scales. A deeper grasp of these parameters, along with the sources of GWs, is crucial for the accurate modeling of their effects on the atmosphere's mean state. In this study, we examine lidar data from two sites, Kühlungsborn (54°N, 12°E) and ALOMAR (69°N, 16°E), to investigate the spectra of GW fluctuations in the stratosphere and mesosphere. Our detailed investigation reveals how GW spectra alter under varying atmospheric conditions, paying particular attention to seasonal and altitudinal variations. The results of our study enrich our understanding of atmospheric energy transfer, bridging theoretical concepts with empirical observations.

 

This study is concerned with time-height variations of the turbulence echo power observed with the equatorial atmosphere radar (EAR) located at 100.32°E, 0.204°S, Kototabang, Sumatera, Indonesia on December 15, 2005. We especially focus on a relation between the radar reflectivity (η) and the background refractive index gradient dn/dz=M as well as the behavior of atmospheric turbulence, where the atmospheric stability (occurrence of turbulence) is represented by the Richardson number (Ri). The vertical echo power (So) is sampled at a 150 m height interval with EAR. Intensive radiosonde soundings with hourly launches were also simultaneously conducted at the EAR site, which provides a unique data set for time-height variations of atmospheric parameters. We measured profiles of temperature (T), relative humidity, pressure, and horizontal wind velocity (U) every two seconds, where the balloon ascending speed was about 5-6 m/s. Because the original radiosonde data points were not uniform, we applied interpolation for creating a profile with a uniform interval of 10 m. First, we compared time and height structure between So and M2/N2, whose cross-correlation analysis at 3-9 km altitude resulted in a peak value of 0.69. Next, we analyzed Ri every 10 m altitudes from T and U, then, we calculate the percentage occurrence of Ri-KHI (0

Turbulence was responsible for 71% of all weather-related aviation accidents and incidents in the US between 2000–2011 [1], leading to structural damage, injuries and US$200 million in unforeseen costs for airlines each year [2]. With only 14% of turbulence encounters being attributable to convection [3], clear-air turbulence (CAT) is a leading cause of these encounters and thus poses a major risk to travellers. A variety of dynamical mechanisms can be responsible for CAT, including shear instabilities, inertial instabilities and gravity waves; however, differentiating between the distinct roles of each mechanism when more than one is present remains difficult. In fact, it is the precise evolution of these atmospheric instabilities and waves, and their potential for generating CAT, which remain uncertain in our current scientific understanding.

 

In this study, we investigate the relationship between CAT and gravity waves, with a specific focus on tracking the formation of these waves around regions of inertial instability. Previously, [4] showed the emission of inertia–gravity waves following the release of inertial instability using idealised model simulations. Here, we use the WRF model to consider some real-world examples of where regions of low potential vorticity (PV) in the vicinity of the jet stream are associated with inertia–gravity waves. We track the waves as they propagate and investigate whether the causal link found by Thompson and Schultz can be observed in more realistic simulations.

 

We present results from several case studies exhibiting this behaviour, identifying the sources of the gravity waves observed in simulations. The characteristics of these waves will be compared to those in the idealised model simulations, and gravity-wave parameters will be calculated. Finally, we widen our analysis by examining the broader upstream pattern that contributes to the development of the initial inertial instabilities and explore the different regimes under which these phenomena occur.

 

References:

 

[1] Gultepe, I. et al. (2019), "A review of high impact weather for aviation meteorology." Pure and Applied Geophysics, 176, pp.1869–1921.

 

[2] Williams, J. K. (2014), "Using random forests to diagnose aviation turbulence. " Machine Learning, 95, pp.51-70.

 

[3] Meneguz, E., Wells, H. and Turp, D. (2016), "An automated system to quantify aircraft encounters with convectively induced turbulence over Europe and the Northeast Atlantic." Journal of Applied Meteorology and Climatology, 55(5), pp.1077–1089.

 

[4] Thompson, C. F. and Schultz, D. M. (2021), "The release of inertial instability near an idealized zonal jet." Geophysical Research Letters, 48(14), e2021GL092649.

This study estimated the turbulent kinetic energy dissipation rates (ε) in the troposphere and lower stratosphere as well as the mesosphere from the Program of the Antarctic Syowa Mesosphere‐Stratosphere‐Troposphere/Incoherent Scatter radar (PANSY radar). It is shown that the seasonal variation of ε in the lower stratosphere is likely connected to gravity wave (GW) activity. As for mesospheric ε, the weakening of polar mesosphere winter echoes (PMWE) and ε are observed after minor stratospheric sudden warming (SSW) in the Southern Hemisphere in 2019. This is likely due to the modulation of gravity wave (GW) propagation by the minor SSW, resulting in less GW breaking, which is the main source of the turbulence.

Turbulence plays a crucial role in atmospheric dynamics and has implications across various fields. Wind profiling radars operating at very high frequencies offer promise in measuring turbulent kinetic energy (TKE). However, the widely used spectral width method often yields unrealistic negative values, especially in strong wind conditions, due to overcorrection of non-turbulent factors. The Cochin University of Science And Technology (CUSAT), Cochin, India operates a 205 MHz ST radar, equipped with an active phased array consisting of 619 three-element Yagi-Uda antennas arranged in an equilateral triangular grid. By utilizing the full capabilities of ST radar CUSAT, we tested various antenna configurations and estimation methods to address the issue of negative TKE values, in the troposphere as well as the lower stratosphere. The experiment conducted on March 6th, 2024, included traditional single beam width, symmetric beam width with different array configurations, and asymmetric beam width. Our study revealed significant variations in observed spectral widths across different antenna configurations. These findings offer valuable insights into improving the accuracy and reliability of TKE estimates in the tropics, particularly in challenging atmospheric conditions, thereby advancing our understanding of turbulence dynamics.

Since more than 40 years mesospheric radar echoes are observed in the VHF range, e.g. around 50 MHz radar frequency.

 

Two different mesospheric phenomena are most frequently observed, which are the summer echoes and the so-called winter echoes (MSE and MWE, and PMSE, PMWE for polar locations, respectively). While the summer echoes are related to reduced electron diffusivity due the presence of charged ice particles around 84km altitude, the generally much fainter winter echoes typically occur between 50 and 85km height.

 

Specifically in the last two decades PMWE gained interest and case studies as well as statistical analysis of their occurrence have been published.

 

Winter echoes are most frequently observed around the equinoxes and show a clear diurnal pattern, which is related to the available electron density controlled by solar and geomagnetic activity.

 

Given the remaining open questions on the cause, their formation and propagation dedicated sounding rocket campaigns have been performed in the last few years.The dependence of the PMWE visibility with the VHF radar MAARSY on the ambient electron density has been investigated in depth with the co-located partial reflection radar Saura for the solar minimum conditions.

 

Besides a minimum required electron density neutral dynamics are assumed to play a crucial role for the formation, i.e. creation of turbulent structures of suitable scales and their transport. In this study we will analyze radar observations of PMWE in northern Norway using MAARSY multibeam experiments and connect them to background dynamics using the Saura partial reflection radar as well as ECMWF renanalysis data.

 

Polar Mesosphere Summer Echoes (PMSE) have been observed for more than 30 years with 50-MHz VHF radars at various locations in the Northern Hemisphere. Continuous observations of PMSE are conducted on the northern Norwegian island of Andøya (69.3°N) using the ALWIN radar (1999-2008) and MAARSY (since 2010). The same kind of PMSE measurements began in 2004 in the southern hemisphere with the Australian Antarctic Division's VHF radar at Davis Station in Antarctica (68.6°S), which is at an opposite latitude to Andøya. As the radars at both sites are calibrated, the received echo strength of PMSE from more than one decade of mesospheric observations on both hemispheres could be converted to absolute signal power, allowing a direct comparison of the measurements. The analysis of PMSE observations from the two radar sites over 23 boreal summers and 15 Austral summers indicates comparable PMSE signal strengths. However, there is a noticeable difference, with significantly fewer PMSE occurrences in the southern hemisphere compared to the northern hemisphere. Compared to Andøya, the PMSE season over Davis starts about 7 days later on average and ends 9 days earlier, resulting in a duration that is 16 days shorter. PMSE over Davis occur less frequently but with greater variability in seasonal, diurnal, and altitudinal occurrence. Specifically, PMSE over Davis reach maximum altitudes approximately 1.5 km higher than those observed over Andøya.

Turbulent mesospheric echoes are observed usually during daytime at the Instituto Geofísico del Perú's Radio Observatorio de Jicamarca using the high-power large-aperture radar at specific campaigns. Since 2022, with the inclusion of two new sold-state transmitters, new operational modes were added in order to obtain ionospheric parameters routinely.

 

As part of this unattended mode, low range resolution mesospheric echoes were detected, and we were able to estimate the zonal and meridional winds at the detected ranges.

 

In the present study, we will present the preliminary results of the climatology of the winds estimates obtained from the mesospheric winds and compared with other systems installed at the same location.

 

 

Several non-specular meteors studies have been conducted with the high-power large-aperture (HPLA) radar at the Instituto Geofísico del Perú's Jicamarca Radio Observatory. Studies of interest are the ones that use the high-power meteor trails to estimate Mesosphere and Lower Thermosphere (MLT) winds (80 - 120 km) by combining 3 or more received signals using interferometry. The main limitation with this technique is the strong presence of the Equatorial ElectroJet (EEJ) between 90 - 110 km.

 

A novel method to extract non-specular meteors trails based on their shape through a computer vision model called RetinaNet in presence of the EEJ is presented in this work. The obtained MLT winds obtained with the HPLA is compared with the routinely winds obtained with the specular meteor radar SIMONe collocated with the Jicamarca radar.

Equatorial Spread F (ESF) is a phenomenon that occurs in the magnetic equatorial ionosphere and can disturb the GNSS and radio signal propagation at night. This phenomenon is caused by depleted areas of plasma density (also known as bubbles) that begin at the bottom of the ionospheric F region. The Jicamarca Radio Observatory (JRO) in Peru has made it possible to study ESF using the 50 MHz Jicamarca ionospheric radar in the low-power mode called JULIA (Jicamarca Unattended Long-Term Studies of the Ionosphere and Atmosphere). The radar detects backscattered signals caused by the ESF structures, generating Range-Time-Intensity (RTI) power maps that show the temporal and spatial (altitude) occurrence of ESF. The Madrigal database contains over 20 years of RTI maps measured at Jicamarca, allowing us to identify different ESF morphological patterns or structures, such as Bottom-type, Bottomside, and Radar plumes. These patterns show the evolution of the ESF and can be used to forecast it. However, manually identifying these structures is a time-consuming process. To overcome this issue, a deep learning model using the U-Net convolutional neural network architecture was implemented to segment and classify four morphological patterns automatically. The model was trained using various features such as backscatter power, the F10.7 solar flux index, the disturbance storm time index, the Moon phase, the vertical drift, the zonal drift, and the statistical texture information of backscatter power and vertical drift. The proposed model achieved an accuracy of 90.08% in segmenting and classifying the structures. This model was applied to the RTI database, allowing us to obtain climatology statistics for each morphological pattern.

 

VHF radar data have revealed field-aligned irregularities (FAIs) in the nighttime F region. Many observations have demonstrated a close correlation among FAI, Spread F, and medium-scale traveling ionospheric disturbances (MSTIDs) in the middle-latitude nighttime ionosphere. In 2015, we reported the occurrence climatology of F region FAIs in the middle latitude covering the period from 2010 to 2014, as observed by a coherent scatter radar in Daejeon, South Korea. The high occurrence of nighttime FAIs during local summer was consistent with the high occurrence rate of MSTIDs during that season. However, the dependence of the FAI activity on the solar cycle did not aligned with MSTID activity. This study investigates occurrence characteristics of F-region FAIs, using the Korea VHF radar data from 2010 to 2023, encompassing more than one solar cycle and idendifies the morphological relationship between MSTIDs and F-region FAIs in the middle latitude.

 

Space weather disturbance triggered by solar wind/magnetosphere propagates from high latitude to low latitude, which is first detected over Mohe, China. In this paper, calcium ions which observed by the Ca+ lidar of meridian project are used as tracers of ionospheric dynamic processes. The occurrence rate of thermosphere-ionosphere Ca+ (TICa+) is 75% in summer and 41% in autumn at Mohe. The TICa+ may be attributed to the combination of geomagnetism and convection. The lower density in autumn than in summer maybe due to seasonal variations in growth rates of Perkins instability. During coronal mass ejection (CME) event on 5 November in autumn, TICa+ has a high Ca+ density, much higher than other autumn days. The TICa+ at Mohe maybe related with strong magnetic storms, convection together and Spread F together.

The ion temperature is an important parameter for ionospheric detection. Since the Ca+ ion layer with fine structure of 80-300 km has been observed, it has become possible to detect ion temperature in the E-F region via metal ions with ground-based lidar. However, existing Ca+ ion lidar systems can only detect Ca+ layer density. To address this, we upgraded and modified the Ca+ Optical Parametric Oscillator (OPO) Lidar system at Yanqing Station, Beijing (40.41°N, 116.02°E) to emit lasers at three frequencies for Ca+ ion Doppler detection. This development represents a pioneering step in measuring ion temperatures by lidar in the E-F region. Preliminary results on density and temperature in the E region show that reasonable detection temperatures at 90-105 km under the condition of smooth changes in Ca+ ion morphology, aligning well with satellite-based observations and model-derived temperatures in the E region. Furthermore, a preliminary detection of temperature at 200-300 km in the F region has also been carried out.

 

The equatorial plasma bubbles (EPBs) are frequently observed with quasi-periodicity (QP). Ionosonde and airglow photometer observations often reveal periodic variations, which appear to be associated with the periodic nature of EPBs. Conversely, ionosonde and airglow observations exhibit QP variations without EPB presence. This study aims to investigate whether ionosonde observations exhibit characteristics of atmospheric gravity waves (AGWs) and explore potential commonalities among ionosonde observations displaying quasi-periodic variations linked with EPBs. By leveraging scanning mode observations from the 30-MHz Gadanki Ionospheric Radar Interferometer (GIRI) to estimate EPB inter-bubble spacing and utilizing high-resolution data from a collocated digisonde (DPS-4D) to infer wave-like variations preceding EPB onset, we observe downward phase propagation in height as well as in electron density, suggestive of AGW influence. The inter-bubble spacings of EPBs are found to be in the range of 200-660 km. Additionally, there is notable alignment between the horizontal wavelength of wave structures and EPB inter-bubble spacing has been observed, which indicates a potential role of AGWs in EPB initiation. However, similar wave-like variations are also observed on non-event days, suggesting that specific orientations may be required for wave structures to polarize and seed EPBs.

 

The ionosphere and thermosphere variability is expected to change within long periods because of different reasons like e.g. the impact of climate change. Various studies found such long-term changes in different parameters of the ionosphere and thermosphere. They depend on factors such as magnetic latitude, seasons, time of the day, etc. However, analyzing these changes poses several challenges. The most significant challenge is determining an appropriate model for the ionosphere parameters and its driving parameters. The most commonly used approaches to describe the dependency between ionosphere/thermosphere parameters and the driving parameter are linear and polynomial fits to data sets spanning several decades. A few studies indicate that the commonly used F10.7 cm index is not the ideal input parameter for this purpose. This work contributes to the debate on the best choice of fitting models and solar EUV flux index, while also evaluating the stability of the NmF2 dependence on solar EUV flux throughout different solar cycles.

 

Hourly values of the peak electron density of the ionospheric F2-layer (NmF2) from the ionosonde at Juliusruh station (54.6°N, 13.4°E) are analyzed. The analysis period is between 1957 and 2023. Geomagnetic perturbations are removed based on kp index with a threshold of 3. Linear regression and 3rd order polynomial fit models dependent on different solar EUV flux indices (MgII, F30, and F10.7) are generated for each solar cycle and for winter (January), summer (July), and two equinox months (March and October) separately.

 

The coefficient R^2 is used to measure the quality of the NmF2 model dependent on the solar EUV flux proxies. It shows a well-pronounced local time dependence in January with R^2 value being maximum around noon hours. During the other months, R^2 is rather constant throughout the day. R^2 is highest for F30 and MgII in general and especially during winter noon conditions. Comparing the slopes of the model curves for the different solar cycles, a clear decrease in the slope with each solar cycle becomes visible. We conclude that the best solar EUV flux proxies for describing the NmF2 dependence at all LT hours are MgII and F30. In addition, the response of NmF2 to solar EUV flux shows a clear long-term change as the model slope decreases with time for each solar cycle.

 

This work is concerned with the statistical analysis of the long term observations of the Equatorial Atmosphere Radar (EAR, Indonesia (0.20°S, 100.32°E)) observation from June 2001 to December 2019, with particular focus of the aspect sensitivity of the echo power and the vertical wind component. We define the aspect sensitivity (AS) as the ratio of the echo power in the vertical beam with the mean echo power among the four oblique beam directions tilted by 10°. By considering the high humidity at 3-5 km of lower troposphere, a relatively dry level at 8-10 km in the upper troposphere and the sharp change at the 16-18 km of tropopause, we examine the relation between AS and the horizontal wind components. In the lower troposphere, a linear regression shows a positive slope 0.41, indicating that the large eastward winds correspond to high AS values. On the other hand, high AS values correlate with the large westward winds in the upper troposphere and tropopause regions with a negative slope of –0.49. We also discussed the long-term vertical velocities W measured directly from the vertical beam and the combination of symmetrical oblique beams.

Meteor radar observations provide wind data ranging from 80 to 100 km altitude, while the Michaelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) onboard the Ionospheric Connection Explorer satellite offers wind data above 90 km altitude. This study aims to generate wind profiles in the mesosphere and lower thermosphere by combining the winds derived from meteor radar and MIGHTI observations over the Korean Peninsula from January 2020 to December 2021. The wind profiles derived from the two instruments are continuous at night, but they show discrepancies during the day. The atomic oxygen 557.7 nm (green line) emission intensity measured by MIGHTI peaks at approximately 100 km during the day and 94 km at night. The vertical gradient of the airglow volume emission rate is more pronounced during the day. These differences can cause day-night differences in the MIGHTI wind retrieval accuracy, potentially leading to discrepancies during the day.

Accurate estimates of atmospheric humidity profiles can greatly improve decision-making and planning in various scientific and application fields, including weather forecast, climate change projection, aviation safety, agriculture planning, hydrological hazards and environmental monitoring. Several methods for continuously monitoring the time-height variations of humidity in the low-to-middle troposphere (up to about 10 km) have been proposed using a wind profiling radar (WPR) regardless of various meteorological conditions.

 

Using the Equatorial Atmosphere Radar (EAR) in Kototabang, west Sumatra, we have applied a method for estimating the specific humidity, q, which was originally developed with the MU radar. We employed a relation between the refractive index gradient squared, M2, and the turbulence echo power (the volume reflectivity). The key technique here is the Radio Acoustic Sounding System (RASS) for simultaneously monitoring profiles of the temperature, T, as well as the Brunt–Väisälä frequency squared N2. This method, however, determined only the magnitude of |M|, therefore, delineation of its sign is the critical problem. The other uncertainty is an accurate estimation of the filling factor of turbulence within a radar range volume. Simultaneous q profile derived from radiosonde data was used as an initial condition. From the continuous measurements of the precipitable water vapor (PWV) with a GNSS receiver, we constrained the integrated amount of water vapor so as to delineate a better estimate of the sign of |M|.

 

The other unique method of the q estimate has been recently developed by using the two-cascaded steps of several machine learning (ML) models, which processed the basic moment values of the Doppler spectra, such as the power (first moment), wind velocity (second moment), and the spectrum width (third moment), from WPR. Radiosonde data is used as a reference.

 

This study combines the above two methods to estimate a q profile by applying various ML algorithms to the basic parameters observed with EAR-RASS measurements, such as T , echo power and spectral width . These parameters have a relation with turbulence energy dissipation rate, volume reflectivity of the turbulence echo, and the volume filling factor of turbulence layers, which are essential in calculating specific humidity .

 

We processed the EAR-RASS data collected between 28 August until 3 September 2016. First, we removed clutter echoes and outliers, and interpolation was done when necessary, then, the data is converted into an appropriate scale. As a reference and label for ML inputs, we use q from the ERA5 global reanalysis and radiosonde data launched at the EAR observatory. We examined performance of several ML models, such as Random Forest, Gradient Boosting, XGBoost, and Artificial Neural Network (ANN). Exploring ML models for the atmospheric parameter prediction has been becoming very active. Our study shows that the ML estimation of q by involving RASS temperature data improves reliability and performance compared to the earlier methods, while maintaining comparable accuracy.

Since 1989, the Universidad de Piura (UDEP) has operated several facilities for MST research. The site where the instrumentation is deployed is now named “Estación Científica Ramón Mugica” located inside of UDEP campus. It is located in Piura (05°10’14” N, 80°38’19” W) on the northern coast of Peru. Piura area is the most western area of South America (SA), and it is between the geographic and magnetic equatorial lines. This area is also the continental core zone more impacted by the climatic phenomenon of El Niño-Southern Oscillation (ENSO) in SA. Our first facility was an ST (Stratosphere-Troposphere) wind profiler radar (50 MHz) with a 100 m x 100 m COCO (Collineal Coaxial) antenna to study the ST dynamic between about 2 – 20 km related to ENSO. It was installed in 1989 as part of a project developed by NOAA. ENSO events in 1992 and 1998 were observed using this system. In addition, this radar system was also configured to observe the ionospheric region (80 – 120 km). For the first time, echoes from the E region were detected above the Piura area, just out of the magnetic equator. Currently, the system is being used to detect meteors and the E-region echoes. Since 2021, the mesospheric and lower-thermospheric (MLT) dynamics above Piura have started to be studied with a newly developed and installed spread-spectrum multi-static radar (SIMONe-Piura). This system allows the estimation of horizontal wind fields with horizontal and vertical resolutions of a few tens of kilometers and a few hundreds of meters, respectively. Other facilities at Piura site are: (a) a GNSS receiver for Scintillation measurements installed in 2023 by Helmholtz Centre Potsdam of GFZ German Research Centre for Geosciences, (b) an Ionosonde receiver installed in 2022 by Jicamarca Radio Observatory (ROJ) of Geophysical Institute of Peru (IGP), and (c) a magnetometer installed also by ROJ.

 

Operations at the National Centre for Atmospheric Science (NCAS) Capel Dewi Atmospheric Observatory (UK), which was home to the 46.5 MHz Aberystwyth MST Radar, permanently ceased on 2nd April 2024. The MST Radar had been in operation since 1989, with Doppler Beam Swinging (DBS) ST-mode observations being made on a quasi-continuous basis since late 1997. Vertical beam M-mode observations were added to the standard measurement cycle in 2005. Other instruments operated at and near the site include surface met sensors, surface winds sensors, a laser ceilometer, and a sky-camera. This purpose of this poster is to draw attention to the fact that data collected at the Observatory remain openly-accessible (under a UK Open Government Licence) through the Centre for Environmental Data Analysis (CEDA). The MST radar data products include spectral, radial, and Cartesian/Cardinal (which provide data products, such as the three-dimensional wind vector, that have been derived from observations made in multiple beam-pointing directions). More details can be found at the legacy website, https://mst.nerc.ac.uk/ .

Atmospheric waves and tides dominate the dynamics of the mesosphere and lower thermosphere (MLT) regions. The atmospheric coupling in these regions depends on natural surface phenomena and the interaction of the Earth with the Sun and the Moon. These atmospheric interactions have been studied using neutral wind estimations obtained from radars or satellites. Since 2019, wind measurements of the MLT region have been carried out in Peru using a specular meteor radar system named SIMONe. Investigations have been conducted to describe the behavior of atmospheric disturbances at low latitudes. The present research aims to analyze wind prediction estimates for two days into the future. This analysis considers techniques such as missing data imputation with the Expectation-Maximization algorithm, time series decomposition with the Variational mode decomposition algorithm, modeling with the Long short-term memory neural network algorithm, and the Optuna hyperparameter optimizer. Subsequently, the estimation results are compared with the actual wind measurements series and with a persistence model. The mean square error and Spearman correlation metrics are used for the comparison. Another objective of this study is to demonstrate that the proposed model is better than the interpolations made with a model of dominant harmonics based on the MLT climatology over Peru. The model accuracy depends mainly on the correct decomposition of the time series; this can be fundamental for future analysis related to tides and atmospheric waves. Finally, the results showed that the proposed model performs better than the persistence model and the climatology interpolations.

The Chinese Meridian Project has constructed a comprehensive atmosphere observation system, mainly consist of lidars and other collaborative instruments. From phase one of the project to phase two, a variety of lidars has been deployed to measure atmosphere parameters, such as temperature, density, and wind. The instrument configuration can cover nearly the whole height range from near Earth surface up to 1000km. Also, many meteor radars, MST radars, optical interferometers were deployed. All these instruments work collaboratively, making an unprecedent comprehensive measurement of the atmosphere. Collocated measurements from lidar and meteor radar show good agreement, while some discrepancies need further investigation.

The Zephyr multistatic meteor radar network has concluded its initial hardware development and node deployments throughout Colorado’s front range, and efforts are now focused on wider expansion and deployments. Besides successful wind field estimations using single transmit-receive (rx-tx) links, major technical accomplishments so far include estimates of meteor trail orientation using fully polarimetric rx-tx links, utilizing commercial airplanes as calibration targets via ADS-B, and the design of easily manufactured receivers of reasonable cost.

 

The Zephyr network is similar to other multiple-in, multiple-out (MIMO) continuous coded wave radar networks, but with additional fully polarimetric capability to enable the collection of a complete scattering matrix at each timestep of observation. The network currently consists of a 6-channel transmitter, 3 deployed receivers, and 3 more receivers under deployment. With a center frequency of 31.25 MHz, each transmitter element radiates a unique pseudorandom code at 500 W. The network is scoped to grow to 3 transmit sites and at least 24 receivers scattered throughout the front range of Colorado and beyond.

 

While efforts over the last five years have focused on hardware development and preliminary science results, a recently submitted NSF DASI Track II proposal outlines plans to expand the network. Expansion includes deploying additional transmitters and receivers, creating scalable digital infrastructure for wider data assimilation and easier public access, and developing retrieval techniques that leverage additional information inherent to a large MIMO network. Additional information includes assimilation of observations across many links, higher observation densities and counts, and utilizing the increased geometric diversity. Additional nodes covering the same volume allows for the specular observation of meteors with trail orientations that would otherwise be missed, and the resulting increase in measurement density would greatly improve wind field estimations. This poster details the accomplishments, current state, and future plans of the Zephyr meteor radar network in Colorado.

Supported by the second phase of Chinese Meridian Project (Meridian Project Ⅱ), we constructed the Chinese new VHF antenna arrays for atmosphere and ionosphere observations at low-latitude of China. The official name of this radio system is Qinzhou MST radar, and we also call it Chinese Low-latitude Atmosphere Ionosphere Radar (CLAIR). It is a dual-radar system, consisting of one standard MST radar working at 50 MHz frequency and one dual-frequency array of smaller aperture. The CLAIR began to construct in Sep. 2019 and completed in Mar. 2024. The Qinzhou MST radar/CLAIR is located in Qinzhou, Guangxi, China. Actually, the CLAIR consists of two independent radars, one typical MST radar operated at 50 MHz frequency (CLAIR A) and one dual-frequency radar working at 160 and 200 MHz frequencies (CLAIR B). Preliminary observations have been recorded the echoes from troposphere, stratosphere and mesosphere, as well as the scattered echoes from ionospheric E- and F-region.

 

The continuous development of digital array phased array technology has greatly improved the performance of new MST radar. We have developed the D4 technology -- Dual-level Distributed Dual-polarization Digital beamforming technology, which can maximize the preservation of the spatiotemporal and two-dimensional information of the original echo signal, effectively solving the reliable transmission and multi beam formation problems of multi-channel and high-speed I/Q data in MST radar. The first level DBF mainly completes the reception, analysis, amplitude and phase weighting of fully polarized channel I/Q data, forming any number of sub-beams. The sub-beam I/Q data is encapsulated and sent to the second level DBF through a high-speed communication interface. This process can reduce the original I/Q data rate by several times the number of primary DBF channels/sub-beams, reduce the original I/Q data rate and error rate of broadband big data transmission, and improve the reliability of data transmission. The second level DBF mainly weights the sub-beams of the first level DBF to form the final desired number of main beams, and packages the data and sends it to the signal processing subsystem for subsequent processing through a high-speed communication interface. This process can further reduce the I/Q data rate, thereby reducing the I/Q data rate and transmission error rate, providing basic conditions for real-time reception and calculation of subsequent signal processing. This technology has been perfectly realised in China's "Meridian Project II" and has been successful.

 

We have recently implemented a Low lAtitude long Range Ionospheric raDar (LARID) at Dongfang (19.2°N, 108.8°E, dip Lat, 13.9°), China, for monitoring ionospheric variabilities over a large longitude region from Africa to Pacific, especially over the oceans where ground-based observations may suffer from data gaps. The LARID consists of two high frequency (HF) coherent backscatter radars, looking toward east and west respectively. Here we present some results by the LARID, with main focus on its capabilities, advantages and limitations in monitoring ionospheric variability. The results show that the LARID can detect various ionospheric variations at low latitudes, including (1) sequentially generated equatorial plasma bubbles over a longitude span of ~80°, (2) near-range E region irregularities drifting more than 1000 km, (3) ionospheric background information retrieved from ground scatters, (4) travelling ionospheric disturbances, and (5) sporadic E structures reflecting HF radio waves at low elevation angles. It is demonstrated that the LARID provides an important tool for investigating different types of ionospheric variabilities over a broad region, and will contribute significantly to the regional ionospheric weather forecasting. Further, a bi-static LARID system combining the present one and a future one in the American sector, which may have the capability to simultaneously monitor the low latitude ionospheric variability around the globe, is proposed.

The SIMONe specular-meteor-radar networks are designed and used extensively to study specular-meteor echoes and deriving parameters from these observations (e.g. mean winds).

 

During the usage of these instruments we are also able to observe a lot more different types of echoes besides the specular-meteor echoes that are currently not used on a routine bases but are interesting targets for further studies.

 

Some studies on such echoes were already done in a single event based analysis (e.g. Huyghebaert et al. 2023 https://doi.org/10.1029/2023ja031682).

 

These types of echoes (mainly non-specular meteors, E-region, Aurora, PMSE and EEJ echoes) typically last much longer than the specular-meteor echoes, which typically last far less than a second.

 

As these echoes typically have a relatively small spectral-width, it is more efficient to detect and store them in the spectral-domain.

 

We are proposing a method that allows to efficiently detect this echoes and store them much more space efficient than just saving the raw data making a further analysis and saving the data on a regular basis much easier.

 

This method might also be applicable to other radars observing similar echoes.

The further understanding of the vertical coupling between the upper and lower atmosphere has become increasingly important, especially in the Tibetan Plateau, a global climate-sensitive area referred to as the Third Pole. A new powerful MST radar and lidar system was established to obtain the atmospheric wind field profiles, temperature, and density of the whole neutral atmosphere. The lidar system is also capable of conducting observations both day and night. The lidar system's altitude coverage for the temperature observation is 15-105 km at night, 30-50 km, and 80-110 km during the daytime. As for the wind field, the lidar system can well fill the gap of the MST radar in the altitude range of 20-60 km at night and 20-40 km during the day. The combination of the two powerful and co-located observation apparatus will play an essential role in resolving the two transition regions in the atmosphere with high resolution: the upper troposphere-lower stratosphere (UT-LS) and the mesosphere-lower thermosphere (MLT) regions. This comprehensive system can monitor upward transport and convection, characterize the whole atmosphere over the Tibetan Plateau, and reveal the vertical coupling process between the lower atmosphere, the middle and upper atmosphere, and the ionosphere.

 

A quasi-biennial oscillation (QBO) disruption is a very rare phenomenon in which QBO westward wind is temporarily interrupted by the occurrence of a band of westward wind in the tropical stratosphere. This phenomenon is important as it could greatly affect the global atmospheric circulation, especially in the mesosphere. Past observational and modelling studies have shown the QBO-varying mesospheric diurnal tide, but the mechanism is still not fully understood. In this study, we report the strong response of mesospheric diurnal tides to the two QBO disruptions that occurred in 2015/16 and 2019/20 and its possible mechanisms. The diurnal tidal winds are observed by a meteor radar chain, consisting of meteor radars located at Kunming (25.6° N, 103.8° E), Wuhan (30.5° N, 114.2° E), Mengcheng (33.4° N, 116.5° E), Beijing (40.3° N, 116.2° E) and Mohe (53.5° N, 122.3° E) in China. These observations provide clear evidence that mesospheric diurnal tides are unusually weakened (by ~-6 m/s) during these QBO disruptions, over Kunming, Wuhan, Mengcheng, and Beijing. By using the Specific Dynamics version of the Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (SD-WACCM-X) and the European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis v5 (ERA5) dataset, the analysis indicates that the QBO wind affects mid-latitude mesospheric diurnal tides by modulating both the solar radiative absorption by subtropical stratospheric ozone (~5 to 0.5 hPa) and the tidal- gravity wave interaction in the mesosphere (~60 to 100 km). Thus, these unexpected QBO disruptions provide an opportunity to better understand the coupling between climate change and middle atmospheric dynamics.

Atmospheric gravity waves (AGWs) generated primarily from tropospheric sources can propagate into the thermosphere and ionosphere where they can cause traveling ionospheric disturbances (TIDs). TIDs can significantly affect the performance of high-frequency (HF) instruments by causing variations in the electron density, maximum usable frequency (MUF) and total electron content (TEC). We investigate the source of TIDs recorded by a quasi-vertical ionospheric sounder (QVIS) located in the Adelaide region (35S, 138E), south-east Australia. The TID signatures were identified in ionogram images at the bottom side of the F layer (z=200-250 km) due to the passage of a wave train with a period of 20 min and horizontal wavelength of 175 km moving southwestward with a velocity of 145 m/s. Neutral atmospheric data and inferred gravity wave parameters are used with gravity wave ray tracing technique to locate the sources of these waves. Buckland Park (35S,138E) medium frequency radar data were used to define the wind field between 70 and 100 km, and data from the whole atmosphere community climate model with thermosphere and ionosphere extension (WACCM-X) were used to define winds between 100 and 250 km and temperature fields from the surface to 250 km. Our ray tracing results suggest that the TID identified by the ionospheric sounder originated from gravity waves generated by tropospheric convection over the South Pacific near Australia.

 

Atmospheric gravity waves are low-frequency transverse waves (periods larger than 10min) having frequencies low enough to be affected by gravity. The AGWs play an essential role in atmospheric dynamics, vertical energy transport, and the atmosphere-ionosphere coupling. The AGWs generated in the lower atmosphere propagate upward to the ionosphere where they produce irregularities of the electron density, which are observed as traveling ionospheric disturbances (TIDs). On the other hand, intense ionospheric electric currents and auroral precipitation in the auroral zone can cause AGWs which propagate downward to the mesosphere. In the present study we focus on the medium-scale AGWs with periods 25-100 minutes. We use the ionosonde and meteor radar data from the Sodankylä Geophysical Observatory (SGO, 67°N, 27°E, Finland, MLAT ≈ 64°) located in the vicinity of the equatorial part of the nightside auroral oval. The AGWs at about 90 km altitude were inferred from the wind data of the Nordic Meteor Radar Cluster (Stober et al., https://doi.org/10.5194/amt-14-6509-2021) with spatial/height/time resolution 90km/5km/10min respectively. At the same time, TIDs were detected as variations of the electron density (critical frequency foF2) at the height of F2 maximum (hmF2, 200-350 km) in the data of SGO ionosonde operating with 1-min time resolution. We present 4-years (2020-2023) statistics of the collocated AGW and TID data to investigate propagation of the waves between mesosphere and ionosphere. In summer (April-September), the waves are suppressed likely due to the strong zonal wind shear at the mesopause (near 90 km altitude). Signatures of the most effective atmosphere-ionosphere interaction was observed in the dark ionosphere conditions in the night time in December-March, however it is not the case during the fall transition in September-November. The results are discussed in association with the atmospheric dynamics and geomagnetic and auroral activity.

In this paper, for the first time, simultaneous atmospheric temperature perturbation profiles obtained from TIMED/SABER satellite and equatorial ion density and vertical plasma drift velocity observations with and without ESF activity obtained from C/NOFS satellite are used to investigate the effect of gravity waves (GW) on ESF. The horizontal and vertical wavelengths of ionospheric oscillations and GWs are estimated applying wavelet analysis techniques. In addition, vertically propagating GWs that dissipate energy in the ionosphere-thermosphere system are investigated using spectral analysis technique. We find that vertical wavelength of GW, corresponding to dominant wavelet power, ranges from 12 to 31 km regardless of the conditions of the ionosphere; however, GWs with vertical wavelengths between about 1 to 13 km are found every day saturated between 90 and 110 km at different longitudinal sectors. Filtering out vertical wavelengths above 13 km from temperature perturbations, ranges of zonal wavelengths of GW (i.e. from about 290 to 950 km) are found corresponding to irregular and non-irregular ionosphere. Similarly, corresponding to dominant oscillations, zonal wavelength of ion density perturbations is found within 16 to 1520 km. Moreover, we find an excellent agreement among the median zonal wavelengths of GW for the cases of irregular and non-irregular ionosphere and ion density perturbations that are 518, 495, and 491 km, respectively. The results imply that seed perturbations due to GW with vertical wavelength from about 1 to 13 km evolve to ion density irregularity and may be amplified due to post-sunset vertical upward drift velocity.

 

In this paper, we study variations in equatorial ionospheric vertical ExB drift during sudden stratospheric warming (SSW) events over Indonesian region. For this study, we have used observations of vertical ExB drift estimated from Doppler shifts of the 150-km echoes observed by the 47 MHz Equatorial Atmospheric Radar (EAR), Kototabang, Indonesia from 2017 to 2019. We have analyzed four SSW events that occurred in the period: February 2017, February 2018, January 2019, and September 2019. Results show that the vertical ExB drifts were highly upward/southward in the morning hours and near zero or downward/northward in the afternoon hours, showing clear semidiurnal variation during the SSW events. The observations also show day-to-day variations, which are found to be governed by planetary-scale variability with periodicity of ~15 days and ~6 days. What is most remarkable is the onset of semidiurnal variations occurring during SSW events were close to the new and full moons, which indicates that the lunar tidal wave effects were highly enhanced during SSW events. These results are first of their kind from Indonesian sector and illustrate the type of variability that SSW can induce in the vertical ExB drift. These results are presented and discussed in the light of current understanding of SSW related coupling processes.

 

Multi-group of strong atmospheric waves (wave packets #1-#5) over China associated with the 2022 Hunga Tonga–Hunga Ha’apai (HTHH) volcano eruptions were observed in the mesopause region using a ground-based airglow imager network. The horizontal phase speed of wave packet #1 and #2 is approximately 309 m/s and 236 m/s respectively, which is consistent with Lamb wave L0 mode and L1 mode from theoretical prediction. The amplitude of the lamb wave L1 mode is larger than that of L0 mode. The wave fronts of Lamb wave L0 and L1 below the lower thermosphere are vertical, while the wave fronts of L0 mode tilt forward above exhibiting internal wave characteristics, which show good agreement with the theoretical results. Two types of tsunamis were simulated, one type of tsunami is induced by the atmospheric pressure wave (TIAPW) and the other type tsunami is directly induced by the Tonga volcano eruption (TITVE). From backward ray tracing analysis, the TIAPW and TITVE were likely the sources of the wave packet #3 and wave packets #4-5, respectively. The scale of tsunamis near the coast is very consistent with the atmospheric AGWs observed by the airglow network. The AGWs triggered by TITVE propagate nearly 3000 km inland with the support of duct. The atmospheric pressure wave can directly affect the upper atmosphere, and can also be coupled with the upper atmosphere through the indirect way of generating tsunami and subsequently tsunami generating AGWs, which will provide a new understanding of the coupling between ocean and atmosphere.

 

Yamazaki et al, (2022) examined the wind shear theory for Es formation using wind-shear observed by ICON/MIGHTI and COSMIC-2 radio occultation (RO) data. In contrast to ionosondes, which measure directly the Es density, RO measures the plasma gradient in the Es layer. So the Es layer height given by the two methods are not always the same. And their results may not be generalized to ionosonde observations. To examine this, we look into the the relationship between the ionosonde-observed Es and the wind-shear observed by ICON/MIGHTI. Our analysis reveals that their relationship depends strongly on the Es intensity (foEs) and altitude (h'Es). For strong Es with foEs>6MHz, 90% are related to negative wind shear when h'Es<115 km, but reduces to ~50% when h'Es>115km. For moderate Es layer with foEs of 3-6 MHz , ~80% corresponds to negative shear when h'Es < 115 km, and drop to 70% when h'Es> 115 km. These results reflect that the formation of strong Es confirms more to the wind-shear theory, while weak Es are more complicated.

 

On 15 January 2022, the Hunga volcano on Tongan Island produced a massive explosion that disrupted the entire atmosphere. We report horizontal wind perturbations in the mesosphere and lower thermosphere (MLT) as a result of the eruption, measured by five multistatic specular meteor radars located on the west side of South America and northern Europe.

 

In South America, the most notorious signal was an exceptional solitary wave with a large vertical wavelength observed around 18 UT at all three sites, with an amplitude of ∼50 m/s mainly in the westward direction. The wave was characterized as traveling at ∼240 m/s, with a period of ∼2 hr and a horizontal wavelength of ∼1,440 km in the longitudinal direction, away from the source. The perturbation is consistent with an L1 Lamb wave pseudomode and the so-called Pekeris mode.

 

The extent of such a signal is investigated using the European systems. To do this, the signal characteristics are studied separately as it propagates westward and eastward. The winds display dominant eastward perturbations reaching distances of up to 25,000 km, with high altitudinal coherence, consistent with the South American signal. Additionally, weaker westward perturbations, propagating faster, are identified. Throughout the study, the longitudinal and transverse horizontal wind decomposition approach is systematically used. This approach shows benefits over the traditional zonal and meridional decomposition for studying wind perturbations originating from localized sources, such as extreme geophysical events.

An all-solid-state narrowband lidar system for the simultaneous detection of Ca and Ca + layers has been developed at Yanqing station(40.41 ◦N, 116.01 ◦E). The uniqueness of this lidar lies in its transmitter, which is based on optical parametric oscillation (OPO) and optical parametric amplification (OPA) techniques. The injection seeded OPO and the OPA are pumped by the second harmonic of an injection-seeded Nd:YAG laser, which can generate coherent light at the wavelength of 786 nm or 846 nm lasers, whose second harmonics in turn generate the 393 nm or 423 nm pulses, respectively, for the detection of thermospheric and ionospheric Ca + and Ca layers. Compared to the conventional dye-based system, this lidar transmitter is a narrowband system (bandwidth < 200 MHz), which has produced a factor of two more output power with higher stability and reliability. The lidar system in Yingqing demonstrated Ca + detection sensitivity of 0.1 atoms-cm−3 for long-term observation and reached a height of ~300 km. A lidar for metal atoms and ions observation was developed at Mohe (53.5°N, 122.3°E) recently. It includes 4 big telescopes (Diameter 1.5m). By using the OPO/OPA Technology, laser systems to generate 393 nm or 423 nm pulses were also developed, and their energy can reach 90mJ. Ca + layers in the F regions (up to 320km) were also observed in Mohe region.

 

The present study is the rarely reported observations of meteor ablation detected by all-sky images system with a filter in near infrared (NIR) band from 715 to 930 nm, operating at Cachoeira Paulista (22.7°S, 45.0°W) and lidar observations of the mesospheric sodium and potassium layers, operating at São José dos Campos (23.1°S, 45.9°W), both observatories in Brazil. The all-sky images system showed the meteor explosion in the mesosphere and a subsequent long-lived meteor trail with more than 14 minutes through the NIR band. On the other hand, the Lidar showed that the meteor explosion occurred in an altitude range from 100 to 95 km with the consequent sodium and potassium atoms enhancement on the background layers. Shortly after the meteor explosion (after approximately 1 minute), a digisonde operating at Cachoeira Paulista detected the appearance of a sporadic E layer. In addition, using GNSS data, an analysis of the generation and propagation characteristics of infrasonic pressure waves excited during meteor entry into the Earth’s upper atmosphere/ionosphere is presented. These results have implications for the use of infrasound measurements as a tool for evaluating the flux of near-Earth objects. In this work we present and discuss several features related to the meteor explosion in the upper atmosphere/ionosphere.

 

All-sky radar measurements provide a unique capability to resolve the spatial structure of E region irregularities over a large zonal region. With the all-sky radar interferometry observations at Ledong (18.4°N, 109.0°E) in Hainan, China, the spatial structure and zonal drift of low latitude E region irregularities over a large region are investigated. It is revealed that the E region irregularities, including both the continuous and quasi-periodic (QP) types shown in radar range-time-intensity maps, occurred most frequently in summer. The continuous type was observed being generated locally without obvious zonal drift. The QP type generally covered ~40-500 km zonally, and consisted of up to 9 (peaking at 3-4) irregularity patches separated by ~20-130 km (peaking at ~60 km). The spatially separated irregularity patches predominantly drifted westward at the speed ~50-200 m/s. Gravity waves were surmised to be a major source for causing the spatially separated structures of low latitude QP type E region irregularities. Further, a case of wavelike structure of E region irregularities elongating more than 200 km zonally, and a case of double layer E region irregularities showing synchronized QP/wavelike features were observed, providing concrete evidence for the gravity wave modulating mechanism for their generation.

ESA's Aeolus satellite was the first Doppler wind lidar in space. It provided high resolution measurements of wind on a global scale, including the hard-to-observe upper-troposphere lower-stratosphere (UTLS) region of the atmosphere. In addition to its substantial benefits for numerical weather prediction (NWP), Aeolus was a uniquely capable platform for studying phenomena such as gravity waves (GWs), the quasi-biennial oscillation (QBO), vorticized volcanic plumes (VVPs) and sudden stratospheric warmings (SSWs).

 

In this presentation, we give a retrospective overview of the Aeolus mission. We introduce the satellite’s measurement geometry and wind detection method, explore the mission’s primary aims and objectives, and demonstrate the potential of Aeolus and its successors for future research within atmospheric dynamics. Notably, we present the first satellite observations of atmospheric GWs using a Doppler Wind Lidar (DWL). We also display Aeolus’ ability to observe the QBO, including the 2019/2020 QBO disruption, and show the benefit of the high vertical resolution of its observations when compared to atmospheric reanalysis. Finally, we consider a range of additional novel applications of Aeolus’ measurement data, and look ahead to its follow-on mission, EPS-Aeolus, due to be launched by EUMETSAT in 2031.

In the present work, we present a statistical analysis of the frequency spectra of vertical velocity W based on Middle and Upper atmosphere radar data collected from 2.025 to 19.875 km altitude during several days per month over 35 years (1987-2022). We calculated the monthly mean frequency spectra from one-day time series with a time resolution of 10 min. We analysed the mean spectral slopes in the band [0.5-6 hours], which is in the core of the period range for internal gravity waves at the MU radar latitude. The statistical results of the spectral slopes using W measured directly from the vertical beam and W reconstructed from radial winds measured from symmetric beams along the North-South and East-West directions show small but perhaps significant differences. We paid a particular attention to the impact of missing data due to outlier rejections and low signal-to-noise ratios (SNR) in the time series and we tested the performance of several spectral estimators (FFT with filled gaps, Lomb-Scargle and Date-compensated Discrete Fourier Transform). These tests allowed us to find the best configuration to minimise estimation bias on slope and variance. The monthly mean spectral slopes of the spectra averaged in altitude show a seasonal dependence with a minimum of ~-0.7 in August and a maximum of ~-1.1 in January. The spectral slopes also show a dependence on wind speed U and are almost flat in summer above 16 km altitude when U is weak (<10 m/s) and when the gravity wave activity (variance) is minimum. The variance is maximum in winter above 12 km altitude and increases with U. Comparisons between the measured slopes and the slopes of some Doppler-shifted model spectra of saturated gravity waves show that Doppler-shifting cannot account for the observed dependence with U. We reveal that the spectral slopes depend on zenith aspect ratio (i.e. ratio between the vertical and oblique echo powers) and power imbalance between symmetric oblique beams to an extent similar to Doppler-shifting. The reason for this dependence requires more studies. However, after correcting for biases associated with mechanisms that produce power imbalance effects, we found that: (1) the spectral slope in the troposphere (when N2<2 10-4 rad2s-2) is in fact almost seasonally invariant (~-0.8) despite the strong variability of U, (2) the spectral slope is highly variable in the stratosphere (when N2>2 10-4 rad2s-2) from ~0 to -1.2 and shows a clear exponential dependence with U up to 70 ms-1 at least. If Doppler-shifting can be neglected, then the variation of the slope with U can represent a real change in the shape of the intrinsic frequency spectrum.

 

Vertical motion (w) of air is an important dynamical variable as it facilitates the study of different atmospheric processes across different scales. This w has embedded the signatures of the prevailing atmospheric dynamics starting from local mesoscale processes right up to planetary scale circulations, all of which can be quantified with appropriate precision and period of observation of w. The upward and downward motion of air parcels are set in place to attain radiative-convective equilibrium in the troposphere. This indirectly controls the weather phenomena over a region in the lower troposphere. And has direct control over the dynamical, radiative, and chemical interactions between the well-mixed troposphere and the stably-stratified stratosphere in the upper troposphere and lower stratosphere (UTLS) region through the transition inversion layer- the tropopause, whose vertical structure and temporal variability manifests the vertical exchange of mass and momentum between the lowest two layers of the atmosphere. These processes, termed as “Stratosphere-Troposphere Exchange” (STE) by the atmospheric science community, play a vital role in determining the climatological features of a region. To quantify all these processes precision in measured w becomes very important, but like any region of interest, having accurate measure of vertical motion of air is very difficult owing to its relative small magnitude compared to the horizontal components of wind. In this aspect, a state-of-the-art, indigenously developed stratosphere–troposphere (ST) radar operating at 206.5 MHz, which is a pulse-Doppler radar at Nainital (29.35°N; 79.45°E) - the region of interest in the central Himalayas, gives direct measurements w which has been used to study the long-term characteristics of vertical air motion and its role in the dynamical processes. Five years (2019-2023) of w measured from the radar vertical Doppler have been characterized. Further w is averaged for each hour of observation in a day. Monthly mean of hourly data shows the presence of downdrafts in the lower troposphere, whereas in the upper troposphere it is the mixture of both updrafts and downdrafts. Weaker downdrafts are observed during the monsoon season. This gives us an insight into the long-term characteristics of w over the region with seasonal variations associated with the various local climatological features. Details of results shall be presented at the upcoming workshop.

 

Vertically-resolved measurements of wind velocity in the middle atmosphere are essential for understanding the global circulation driven by dynamical processes such as gravity and planetary waves interacting with the atmospheric flow. While weather balloon soundings provide regular observations of horizontal wind profiles up to about 30 km altitude, the layer between 30 – 60 km altitude, the so called “radar gap” is poorly covered by observations. The only information on the wind field in this layer available on the regular basis is inferred from horizontal pressure gradients derived from space-borne temperature measurements using geostrophic balance assumption however this does not allow characterizing regional-scale dynamical processes.

 

Here we present Rayleigh-Mie wind lidar, measuring Doppler shift between the emitted and backscattered light by means of a Fabry-Perot interferometer. The wind lidars are deployed at Observatory of Haute-Provence (OHP, Southern France) and at Maido observatory in Reunion Island (tropical Indian Ocean). The instruments are capable of measuring horizontal wind components from the middle troposphere up to 75 km altitude with vertical resolution as high as 100 m and temporal resolution down to 5 minutes. Both lidars have been operated quasi-continuously since 2019 thus providing the first multi-year vertically-resolved time series of wind velocity in the northern midlatitudes and southern tropics.

 

In this study, we present and discuss various scientific applications of the wind lidar observations. We report examples of a weekly and an hourly observation series, reflecting various dynamical events in the middle atmosphere, such as a Sudden Stratospheric Warming events and occurrence of orographic and non-orographic gravity waves. Wind velocity profiles are analysed in conjunction with temperature lidar profiling, radiosoundings, satellite observations as well as meteorological analysis/reanalysis in order to characterize gravity waves and their vertical propagation and filtering.

 

Finally, we present a summary of results of the ESA Aeolus space-borne wind lidar validation using its ground-based predecessor in the frame of a series of dedicated campaigns at both observatories.

 

 

The European Space Agency's Aeolus satellite, equipped with the Atmospheric LAser Doppler INstrument (ALADIN), provides comprehensive global wind profiling, offering valuable insights into convection-induced gravity waves (GWs) in the upper troposphere and lower stratosphere (UTLS). This study analyzes Aeolus-derived wind data alongside ECMWF ERA5 reanalysis, revealing a migrating hotspot of enhanced GW activity. This activity transitions from the Indian Ocean during the Boreal Summer to the Maritime Continent in Boreal Winter, correlating strongly with convective activity as evidenced by variability in outgoing longwave radiation. The results underscore the importance of Aeolus in improving the representation of convective-induced GWs in ERA5, particularly in the under-sampled Indian Ocean region, thus enhancing our understanding of GW phenomena in the UTLS.

 

While the benefits of Aeolus global wind profiling are straightforward, important limitations exist, particularly when studying extratropical UTLS dynamics. We identify and characterize these limitations in our study, focusing on the Range Bin Setting (RBS) of Aeolus. This RBS adjusts dynamically based on seasonal and geographical variations, affecting our ability to measure and interpret gravity wave dynamics accurately.

 

We also examine oscillatory perturbations (OPs) identified in Aeolus data, particularly between 12 and 19 km altitudes, displaying a unique oscillatory signature. These OPs emerge prominently above high-albedo regions such as Greenland and Antarctica. The nature of these oscillations remains unexplained although the dark current anomalies on the instruments (hot pixels) may amplify these oscillations without explaining their inherent characteristics. The absence of these phenomena in GNSS Radio Occultation data suggests that the observed perturbations in Aeolus data are not related to gravity waves but are likely linked to the satellite's specific observational characteristics.

 

These variations introduce substantial uncertainty into our models and highlight the necessity for developing more precise metrics that can reliably detect and interpret such phenomena.

 

Using the Middle Atmosphere Alomar Radar System at Andøya, Norway (69.30°N, 16.04°E), we investigate the absolute momentum flux (AMF) and vertical wind variance (ρw′²) along with intermittencies in the upper troposphere and lower stratosphere (UTLS) during 2017–2022 (6 years). Based on the boundary conditions of the available spectra 30 min (Nyquist frequency), 13 hr (inertial period), and 1 day (based on our interest in maximum long-period oscillations), we characterized them into different period bands. The categorization of the AMF and ρw′² into different period ranges (30 min–2 hr, 2–6 hr, 6–13 hr, 13 hr–1 day, and 30 min–1 day) enables us to study the significance of both short- and long-period waves. Through the investigation of the AMF and ρw′², we wish to determine in detail the gravity wave (GW) characteristics at northern polar latitudes. Furthermore, it is crucial to assess the intermittency as it considerably influences and modifies the GW attributes. Our unique results indicate for both AMF and ρw′²: (a) seasonal variation with minima during summer (May–September); (b) higher magnitude in the upper troposphere (<9.00 km) than the lower stratosphere; (c) short-period components (30 min–2 hr, 2–6 hr) are more intermittent in the entire UTLS; and (d) the long-period components (6–13 hr, 13 hr–1 day) demonstrate lower (higher) intermittency in the upper troposphere (lower stratosphere) in summer implying a plausible wave-filtering mechanism.

 

Radar wind profilers (RWP) are widely used in operational meteorology. In the framework of COST and later as part of EUMETNET, a coordinated but opportunistic network of RWPs has been set up in Europe. It includes both operational and research sites operating at VHF, UHF and L-band frequencies. A central data hub collects, processes and disseminates the data in near real-time. Impact studies based on Observation System Experiments (OSE) and on Forecast Sensitivity to Observation Index (FSOI) have shown a generally positive impact on the forecast skills. For global numerical weather prediction (NWP) models, VHF and UHF systems covering the upper troposphere and lower stratosphere have a larger impact than L-band systems covering the lower troposphere only. In the last few years Doppler lidars (DL) have reached maturity and are increasingly used by national meteorological services (NMS) and research institutions. Mostly limited to the aerosol-loaded boundary layer but with enhanced vertical and temporal resolution as well as advanced scanning and sampling capabilities, DLs are suited for a wide range of operational applications like aeronautical meteorology, air quality or NWP. To ensure homogeneous data quality across the DL network, EUMETNET has set up a centralized processing hosted on the European Weather Cloud based on an open-source code developed by the scientific community. This allows to generate standard vertical profiles of wind from a variety of different scan strategies. OSEs showed that DLs can have a positive impact on NWP up to a few hours lead time.

We introduce a novel approach for wind measurements by incorporating a multi-field of view (Multi FOV) capability into the lidar instruments designed under the Vertical and Horizontal Coverage by Lidar (VAHCOLI) concept. The VAHCOLI instruments are versatile Doppler lidars capable of covering a broad altitude range by utilizing Mie, Rayleigh, and resonance scattering. With the Multi FOV upgrade, we achieve the capability to measure both horizontal and vertical winds between altitudes of 3 and 25 km, relying exclusively on aerosol backscatter. These measurements are enhanced by the narrowband properties of Mie backscatter, in conjunction with our spectral measurement method that employs a novel alexandrite ring laser and ultra-narrowband filters. This approach significantly improves our system's ability to accurately measure three-dimensional winds.

 

Our results highlight the system's effectiveness in detecting small-scale wind asymmetries, emphasizing its importance for atmospheric science, particularly in measuring vertical wind velocities. The introduction of the Multi FOV upgrade, featuring an innovative optical arrangement that allows for rapid switching between different viewing angles, represents a major enhancement in our observational capabilities and allows for an in-depth examination of atmospheric dynamics across various scales.

 

Furthermore, a comparison to winds from ECMWF indicates a significant underestimation of vertical winds by ECMWF, underscoring the VAHCOLI system's accuracy and reliability in capturing complex three-dimensional wind patterns. A validation against Aeolus data, demonstrates a minimal bias. This underlines the potential of ground-based lidar systems to complement satellite observations and advance our understanding of atmospheric phenomena. Our work lays the groundwork for future atmospheric research, providing a valuable tool for validating successors to Aeolus and other spaceborne lidar systems.

 

Overshooting convection due to mesoscale and synoptic scale distributions viz., tropical mesoscale convective system (TMCS) and tropical cyclone (TC) can significantly contribute to the stratosphere-troposphere exchange (STE) processes. During such disturbances, the overshooting clouds can transport the water vapour from the troposphere into the lower stratosphere and if the tropopause temperature is cold enough it will freeze-dry. Such overshooting cloud can also weaken the stability of tropopause in the presence of strong updrafts followed by strong downdrafts in the UTLS region. In addition, the undulation of tropopause height during the formation of these synoptic systems can also in turn lead to the STE processes. Weakening of the stability of tropopause and its undulation may rise to the intrusion of stratospheric ozone-rich air into the troposphere. In this contest, an experiment named as ‘Dynamics of Tropical Cyclone Motion (DynTCM)’ was conducted over Gadanki from 29 April to 3 May 2019 by operating Advance Indian MST Radar (AIR) (operates in VHF range) in full volume-scanning, along with the radiosonde and ozonesonde launches. Volume-scanning mode of AIR can provide full three-dimensional atmospheric dynamics and structures. The experiments were designed by the optimum selection of zenith and azimuth beams, which will have a full volume imaging scan within ~5.5 min. Different plausible mechanisms for the occurrence of stratospheric ozone intrusion into the troposphere (from ozonesonde observations) and its association with different scattering mechanisms (from AIR) during the passage of tropical cyclone ‘Fani-2019’ are investigated in details. Tropopause weakening/break and its modulation associated with turbulence as observed from AIR is found to be the prime candidate for the stratospheric intrusion. An increase of ozone by 50-60 ppbv in the mid-troposphere and 20-30 ppbv on the surface are observed when the cyclone was close to the radar site. Strong downdrafts of ~ 0.75 ms-1 are observed in the vicinity of tropopause well before the occurrence of stratospheric intrusion. It is also supported by the presence of dry air in the troposphere. An increase of mid-tropospheric temperature by 4 K associated with Fani is observed. Radar echoes show isotropic structures near the tropopause, whereas anisotropic structures are observed in the lower stratosphere. These observations quantitatively constitute experimental evidence for the re-distribution of ozone during the passage of a cyclonic storm. The detail results will be presented and discussed in the upcoming workshop.

 

Abstract. The radar echo power of mesosphere–stratosphere–troposphere (MST) radar is significantly enhanced in the tropopause because of specular reflection. On this basis, scientists have proposed the radar tropopause (RT) concept. The RT height calculated by the maximum echo power gradient method differs from the thermal lapse-rate tropopause (LRT) height in July and August in Beijing. This study used Beijing MST radar data and radiosonde data to calculate the RT and LRT heights. The observational data of Bejing MST radar and radiosonde showed that the monthly frequencies of q > 10^-4.2 g/g at the RT height were all greater than 0.2, which indicated that the influence of water vapor could not be ignored when the maximum echo power gradient method was used to determine the RT height. The analysis of radar functions showed that the variation of the q in the middle-upper troposphere can significantly affect the radar echo power through turbulent scattering and specular reflection. The radiosonde observation showed that there is an atmospheric interface with different thermal lapse-rate when the dq/dz has obvious change. If the influence of water vapor is in the LRT, RT and LRT are almost at the same height, which seems to be consistent with the result when the troposphere is assumed to be dry air. Suppose the influence of water vapor is not in the LRT, RT height is different from LRT height, which is the main reason why the distribution of RT and LRT showed significant statistical differences in July and August in Beijing. The result showed that the MST radar echo power in the middle-upper troposphere should consider the influence of water vapor.

 

This study makes use of long-term observations made by the mid-latitude 46.5 MHz Aberystwyth MST radar (52.4 °N, -4.01 °E) and a co-located (Vaisala LD40) laser ceilometer. Use is also made of satellite observations, of photos taken by a sky-camera operated at the MST radar site, and of measurements made by radiosondes launched from other locations. Previous studies have shown that enhanced values of corrected MST radar spectral width, which indicate the presence of turbulence, can be associated with cirrus (e.g. Luce et al., 2010) and altocumulus (e.g. Worthington, 2015) cloud layers. The present study shows that characteristic signatures in MST radar return signal power can also be associated with a wider range of cloud types. Of particular interest are the clouds associated with an approaching warm front, which leads to a decreasing cloud base altitude as a sequence of cirrus, cirrostratus, altostratus, and nimbostratus pass over the radar site. In such cases, enhanced values of corrected spectral width and of radar return signal power are both seen in a layer immediately below the cloud base, as determined by the laser ceilometer. By contrast, enhanced values of corrected spectral width are seen within layers of stratocumulus clouds, but enhanced values of radar return signal power are seen in the layer immediately above them. MST radar return signal powers are expected to depend on the mean vertical gradient of generalised potential refractive index, which is usually denoted by the symbol M. The latter depends on the vertical gradient of potential temperature, on the specific humidity, and on the vertical gradient of specific humidity. Although numerous previous studies have found a good correlation between observed and predicted values at lower stratospheric altitudes, where the effects of humidity are negligible, the same studies have shown a poor correlation at tropospheric altitudes. The present study indicates that tropospheric radar return signal powers can nevertheless give qualitative information about atmospheric structure.

This presentation reviews the 40-year history of the MU radar. The radar, located at the Shigaraki MU Observatory in Shigaraki, Japan, was established in 1984 as the world's first MST radar with an active-phased array antenna system. The MU radar uses VHF radio waves with a frequency of 46.5 MHz (1 MW peak output power). The antenna area consists of 475 Yagi antennas arranged in a 103 m diameter circular array. Fast beam steering and flexibility for various observational configurations characterize the instrument. Researchers from Japan and international communities have used it for a vast area of atmospheric research, starting from the meteorology and atmospheric waves in the middle atmosphere to the plasma/neutral dynamics of the upper atmosphere. The most visible recognition of the MU radar's achievement is its 2015 IEEE Milestone award. Its citation states that “The MU radar enabled continuous and flexible observation of the atmosphere and has contributed to the progress of atmospheric science and radar engineering.” In the presentation, we try to show both the technical and scientific aspects of the contribution.

The new powerful Tibetan Plateau (Yangbajing) MST radar (30.1°N, 90.5°E; 4300 m MSL) obtained atmospheric echoes for the first time on October 18, 2023. It is a fully digital multipolar phased array MST radar with a more flexible detection ability. The Tibetan Plateau (Yangbajing) MST radar operates at 50 MHz. It has a circular array with a diameter of 153 m consisting of 931 3-element crossed Yagi antennas and 800 transmit and receive (T/R) modules. The peak power is 1.92 MW. The power of each T/R module is adjustable with a maximum power of 2400W. This new MST radar has achieved technological breakthroughs in the aspects of full digital two-dimensional phased array technology, multi-polarization observation technology (arbitrary switching of linear polarization, left-handed circular polarization, and right-handed circular polarization transceiver polarization modes), digital multi-beam technology (maximum support for 20 beam simultaneous detection), radar automatic calibration technology, and radar health management technology. The preliminary verification results of the detection capability and data quality of the Tibetan Plateau (Yangbajing) MST radar show that it will play an essential and indispensable role in studying the dynamics of the whole atmosphere over the Tibetan Plateau and in revealing the vertical coupling process between the lower atmosphere, the middle and upper atmosphere, and the ionosphere.

 

Radar observations of the troposphere and lower stratosphere made in southern Australia with the Buckland Park Stratospheric Tropospheric (BPST) 55 MHz VHF radar are presented. The radar operates at a peak power of 48 kW and 15 receiver channels are available. Recently, it has been configured to use a 6x6 sub-section of the array for operation in a Doppler Beam Swinging (DBS) mode. This provides an interesting example of a small DBS radar operating in the lower VHF band. Eight additional 3x3 receive only sub-arrays are available for interferometric operation and Spaced Antenna mode. The system also operates as a 5 receive-channel meteor radar and so measurements of mean winds and wave fluxes measured in the Troposphere, Stratosphere, and Mesosphere are available. We have previously presented measurements made using two VHF radars in Germany, one of them which also used a small antenna array, and the present results extend those. Results are presented and discussed in the context of coupling between these regions of the atmosphere and the potential of such small radars for dynamical studies.

 

Interferometric iMST radar systems are reliant on the accurate estimation of receiver channel phase offsets (i.e. phase calibration) to allow receiver channel phase differences to be measured precisely. These phase offsets may be introduced through mechanisms such as differences in feeder cable lengths, antenna impedances, and receiver characteristics. There exist many techniques for estimating receiver channel phase differences. Direct receiver signal injection allow measurement of phase offsets introduced by differences by the receivers, but excludes the antennas and feeder cables. Terrestrial beacons may be used to provide a known reference signal allowing incorporation of antenna and feeder cable contributions, but may require use of radar resources and also suffer from multi-path effects. Geophysical phenomena, such as partial reflections, meteor echoes and extra-terrestrial noise sources, also allow incorporation of antenna and feeder cable contributions, but require assumptions about the characteristics of the phenomena and the propagation environment. This paper presents a phase calibration technique based on comparing phase differences measured using satellite returns with those expected based on applying specialised general perturbation version 4 (SGP4) propagations of orbital two-line elements (TLEs). The resulting phase calibration estimates are shown to produce lower variance than those obtained using partial reflections, and can be used to monitor long term changes in the phase offsets.

 

In recent years, multi-input multiple-output (MIMO) radar concepts have been implemented in atmospheric radars. Examples of such implementations are the multistatic specular meteor radar systems called MMARIA (Multistatic and Multifrequency Agile Radar for Investigations of the Atmosphere) and SIMONe (Spread Spectrum Interferometric Multistatic meteor radar Observing Network). The MMARIA concept utilizes incoherently the information of links obtained from multiple transmitters and multiple receivers widely separated (Incoherent MIMO), e.g., line-of-sight velocities from different links and different meteor detections. SIMONe implements the MMARIA concept including the information of multiple transmitters closely separated (Coherent MIMO) for each link, e.g., to determine the angle-of-departure of meteor detections. On reception, SIMONe links consist of single or multiple antennas. Therefore, SIMONe uses both incoherent and coherent MIMO configurations. In this work we will present the recent improvements implemented in SIMONe configurations to: increase the location of meteor detections, the amounts of detections, and the detection of over-spread atmospheric targets. In the case of coherent MIMO, a single location solution using the interferometry in transmission and reception simultaneously is measured. Code diversity with long pseudo-random codes has been implemented and processed, to simultaneously detect specular meteor echoes and radar aurora. The improvements in incoherent MIMO consist of processing simultaneously the incoherent information of multiple transmitters, widely separated. These improvements are tested using simultaneous observations of a strong non-specular meteor echo event observed by more than 20 links in northern Germany, including information from a LOFAR low-band receiver located in Potsdam. The resulting improvements in counts and wind quality will be presented and discussed, including the need to improve the phase calibration of interferometric systems at low elevation angles.

 

Over the past several decades, fluorescence lidars targeting metallic layers in the mesosphere and lower thermosphere have seen steady improvement, returning wind and temperature profiles with increasing accuracy, resolution, and maximum altitude. However, the number density of these metallic species decreases rapidly with altitude, and extending the fluorescence lidar technique into the middle and upper thermosphere requires a new approach.

 

In 1997, Gerrard et al. proposed a novel lidar system targeting metastable helium, which exists in measurable quantities in a layer extending from 250 km to 1000 km or above. Recent advances in detector technology have since made this proposed system feasible, and, starting in 2021, a prototype experiment has been under development at the German Aerospace Center in Oberpfaffenhofen. In early 2022, the first profiles of metastable helium were measured, reaching an altitude of 700 km. Subsequent measurements, with increased system performance, suggest that the helium layer extends well beyond these initial results. Most recently, we have expanded the measurement capabilities to allow for spectroscopic measurements of the helium spectrum.

 

We will present an overview of the instrumental setup, report on the recent measurements in more detail, and discuss the future potential of the instrument to measure thermospheric wind and temperature profiles.

 

Human-caused climate change occurs in the whole atmosphere from the ground to the thermosphere. Gathering data with ground based networks and space missions are essential for understanding climate change and monitoring the atmosphere over decades.

 

Lidars are capable to monitor the atmosphere from the troposphere to the thermosphere. In general, such instruments focus onto a limited altitude range for a certain scientific task, such as wind, temperature, metals, ions or aerosols. Moreover, current systems focus on a single method, such as Rayleigh, Mie or resonance scattering applying different technologies. In case of resonance scattering or molecule scattering, such as water vapor, the required wavelength is only addressable by a specially build laser. For a future network of capable lidars, a single technology should cover all applications, regardless of altitude, scattering or scientific goal as far as possible. Since many systems must be build and maintained over long periods of time standardization of the whole chain from the hardware over data analysis to long-term data archives is required. Since multiple systems are required for a network, fast assembling, cost efficiency, and robustness are major goals. Each system must be installed world-wide, operated and repaired. Therefore, each system should be compact, transporatble and self-contained operating in automatic mode after installation.

 

General-purpose ground-based spectral Doppler-lidars are nowadays capable to obtain multiple parameters, such as wind, temperature, aerosols and metals throughout the whole atmosphere out of compact and robust systems with a size of ~1 m3 in automatic 24/7 operation. The project VAHCOLI (Vertical And Horizontal COverage by Lidar) has shown that a networks of such lidars nowadays is capable of applying a bunch of new measurements methods at different altitudes not even possible with existing lidars specialized for a certain application. VAHCOLI is a software-defined, general purpose Doppler-lidar applying advanced general sub-MHz spectroscopy beyond the capability of existing lidars.

 

VAHCOLI bases on a tunable alexandrite ring laser with a line width of 3.3 MHz developed in close cooperation of IAP and ILT. Within the EU-project EULIAA the technology is currently extended to the 386 nm line of Fe for a future UV lidar network including the demonstration of measurements at hard-to reach environments and real-time data processing for data bases such as Copernicus. Due to the deep Fraunhofer-line daylight observations at higher altitudes can be achieved for Rayleigh scattering as has been demonstrated in the past by the IAP for Doppler resonance measurements at this wavelength in the mesosphere. With intra-cavity single harmonic generation of the alexandrite laser the required UV-laser does not need amplification stages. The whole system reduces further in size, electric power and allows eye safe operation from the troposphere to the thermosphere. Whereas EULIAA will be the next generation system, IAP and ILT currently transfer the technology of VAHCOLI already within the project LidarCUBE to the industry. Both activities focus currently onto future lidar networks for the lower atmosphere (Doppler Rayleigh & Doppler Mie) as a demonstration of the feasibility of such networks with nowadays technology.

The EISCAT Scientific Association is currently building EISCAT_3D, the most advanced 3-dimensional imaging radar for atmospheric, ionospheric and near-Earth space investigations. EISCAT_3D is a European Strategy Forum for Research Infrastructures (ESFRI) Landmark in the Environment domain.

 

The fully steerable, tri-static, phased-array incoherent scatter radar is located in Skibotn (inland from Tromsø, Norway), Karesuvanto (Finland, north of Kiruna), and Kaiseniemi (Sweden, west of Kiruna). The transmit-receive array at Skibotn consists of about 10,000 aerials and ten 91-aerial outrigger receivers in the immediate vicinity. The receive-only arrays of Kaiseniemi and Karesuvanto consist of about 5,000 aerials each.

 

Construction of the facility began after the project kick-off in September 2017. First test measurements have been carried out with a single "antenna unit", which consists of 91 crossed-dipole aerials. The next step will be the so-called "PET-7" system, which consists of seven antenna units with full transmit and receive capabilities. PET-7, with 637 aerials with 1 kW power each, will allow for mono-static incoherent scatter radar measurements. Thereafter, EISCAT_3D will gradually expand to fully tri-static operations.

 

EISCAT_3D will eventually replace the EISCAT mainland radars, i.e. the 930-MHz UHF radar and the 224-MHz VHF radar at Tromsø, even though some overlap is foreseen not least for cross-calibration and comparison purposes. The remote receivers at Sodankylä (Finland) and Kiruna (Sweden) are already inoperable due to failures not feasible to repair.

 

The EISCAT Svalbard Radar (ESR) and the Ionospheric Heating facility at Tromsø will not be affected by EISCAT_3D becoming operational.

 

Here we give an overview of the current status and the road ahead.

 

This article introduces the experiment design for Moon imaging based on Sanya incoherent scatter radar (SYISR) and algorithm research in data processing. We conducted Moon imaging experiments using peak power 2MW, frequency 430MHz and two types of waveforms, 13-bit Barker code, and linear frequency modulation (LFM) chirp. Considering optimization of experiment results, the use of an LFM chirp with a bandwidth of 0.3 MHz and a pulse width of 2ms can give higher signal-to-noise ratio (SNR) and resolution for Moon imaging using SYISR. Several key techniques were applied in the experiment design and data processing: 1) for the reliability of the imaging algorithm, the range-Doppler imaging algorithm commonly used in synthetic aperture imaging was applied; 2) to avoid the sidelobe effect of the 13-bit Barker code matched filter, a sidelobe-free filter was used; 3) to mitigate the problem of “north– south ambiguity,” mosaic imaging of the Doppler northern and southern hemispheres of the nearside of the Moon was adopted; 4) the back projection (BP) algorithm was used to obtain focused lunar images. Two types of imaging results are obtained: mosaic images of the northern and southern hemispheres of the Moon and local regional images. The results demonstrate the feasibility and reliability of Moon imaging based on SYISR, which enables potential further lunar geology investigations in the future.

The Low lAtitude long Range Ionospheric raDar (LARID), which consists of two high frequency (HF) radars looking toward the east and west of Hainan Island, respectively, has been developed and installed at Dongfang (19.2°N, 108.8°E, dip lat. 13.8°N), China, under the support of Chinese Meridian Project II. In this talk, we will present the system design of LARID and its first observational results of equatorial plasma bubble (EPB) irregularities. The antenna array of LARID is composed of a west-looking array and an east-looking array. Each array consists of 20 log-periodic antennas for transmission and reception and 4 log-periodic antennas for interferometry, and has a beam steering capability in the azimuth angles of ±24° due the boresight pointing east (or west). Observational results show that the LARID is capable of detecting backscatter echoes from EPB irregularities and the ground, with a distance of 4000 km or more away from Hainan Island. Multiple EPB structures were continuously observed on April 17, 2023, with eastward drifts ranging between 70-130 m/s. Based on ray tracing simulations, the backscatter echoes of EPB irregularities were due to the 0.5-hop and 1.5-hop propagation modes. The distances between the successive EPB structures were estimated ranging between 500-900 km in longitude. The LARID observations, together with other instruments in the East and Southeast Asian sector, provided a clear picture of longitudinal variation of EPBs in 90-125°E. It is expected that the LARID will provide an important tool to study the generation and evolution of EPBs and their short-term prediction in East and Southeast Asia.

The Radio Observatorio de Jicamarca (ROJ) is a facility of Instituto Geofísico del Perú (IGP) that is dedicated to study the ionosphere due to its proximity to the magnetic equator. The observatory has been key to remote sensing research of the troposphere, stratosphere, mesosphere, and thermosphere for more than 60 years. Due to its location research that has been conducted at the observatory is still relevant to new investigations related to meteor science, ionospheric science, and space weather at low latitudes.

 

This work presents the development of two spaced receiving stations, which in combination with the high power-large aperture 50 MHz radar of IGP-ROJ constitutes the J-ARGUS multi-static system, which will provide wavenumber diversity to radar experiments and allow for better estimates of vector Doppler velocities and also enhance the research areas at the ionospheric equator. The first receiving station will be located at the IGP’s Huancayo Observatory, about 170 km east of IGP-ROJ, and the second station will be located at Santa Maria campus of Pontificia Universidad Católica del Perú about 50 km south of IGP-ROJ. Each station will operate over a wide band (~10-80 MHz) and will allow for perpendicular-to-B and oblique radar observations.

 

All-sky meteor radars have become a reliable and widely used tool to observe horizontal winds in the mesosphere and lower thermosphere (MLT) region. The horizontal winds estimated by conventional single-station radars are obtained after averaging all meteor detections based on the assumption of the homogeneity of the horizontal wind in the meteor detection area (approximately 200-300 km radius). In this study, we apply a multistatic meteor radar network consisting of three monostatic meteor radars in Mengcheng (33.36°N, 116.49°E), Feidong (31.76°N, 117.54°E), Wuhan (31.02 °N, 114.45°E) and a bistatic remote receiver in Changfeng (31.98 °N, 117.22 °E). Through synchronized with GPS-disciplined oscillators (GPSDOs) between each site, the Changfeng remote receiver can simultaneously receive Mengcheng and Feidong meteor radar signals. The distances between Changfeng and Mengcheng, and Feidong are 167 km and 44 km, respectively. Compared to typical monostatic meteor radar, the new multistatic meteor radar network shows the feasibility of estimating the three-dimensional (horizontal and vertical) wind field. In addition, the technique allows us to estimate the mean horizontal wind and the gradient terms of the horizontal wind, moreover, the horizontal divergence, relative vorticity, stretching and shearing deformation of the wind field. We are confident that the improved horizontal wind parameters will contribute to improving the understanding of the dynamics in the MLT region.

 

We have recently redeveloped MF radar meteor wind measurements technique by Tsutsumi and Aso [2005], and have significantly improved its time/spatial resolutions by using the MF system at Syowa Station (69S, 39E), Antarctic. Because the duration of meteor echoes is proportional to the square of the radio wavelength, the duration for MF (2-3 MHz) meteor echoes is more than 100 times longer than that of usual VHF (~30 MHz) meteor echoes, indicating that the actual observation time of MF radar meteor measurement is significantly longer and that a more continuous and dense measurement is possible under a geomagnetically quiet condition where MF radio wave can travel without significant absorption or retardation. The redeveloped technique shows that horizontal wind velocities can be estimated with a highly improved time resolution of about 10 minutes in the height region of 80-115 km, and can even be resolved horizontally every 50 km or so within the 10 minutes at around 90 km, the centroid height of meteor echo distribution. Such resolutions are unprecedentedly high as meteor wind measurements [Tsutsumi et al., JPGU 2023].

 

This technique is being applied to MF radars at the northern hemisphere, Saura (69N, 16E) and Juliusruh (54N, 13E), routinely operated by Leibniz Institute of Atmospheric Physics. These radars are well equipped with an interferometer capability with 9 and 6 receiver channels, respectively. We have found that existing archived data of these radar systems can be applicable to the meteor echo analyses as those we have done with the Syowa system. The same techinique is now further being planned to apply to the MF system operated by Arctic University of Norway at Tromso (70N, 19E), by adding digital receiver and antenna system to enable all-sky interferometer measurements. The Saura and Tromso systems are ideally separated to share a common illuminating volume, and are expected to resolve fine time and spatial structures of wind fields, even with much better resolutions than those of recent VHF meteor radar based network measurements.