We investigate the neutral wind and semidiurnal tide (SDT) variations in the mesosphere and lower thermosphere (MLT) during two consecutive minor Southern Hemisphere (SH) sudden stratospheric warmings (SSWs) that occurred unusually early in July-August 2024. Zonal and meridional winds from four meteor radar stations at 50-70 degrees S were analyzed. Zonal winds reversed from eastward to westward between 80 and 100 km altitude during both events, showing a more distinct reversal in the second event. The SDT amplitudes increased and exhibited longitudinal differences around the second event. To elucidate the mechanisms responsible, we analyzed ozone observations from Aura/MLS along with MERRA-2 shortwave heating. Positive ozone anomalies at 10 hPa (similar to 32 km) in the SH polar region around each event coincide with enhanced SDT amplitudes from meteor radars. In addition, the shortwave heating rate shows an enhanced 12-hr component at SH high-latitudes above 40 km during these events, supporting an ozone-related radiative contribution to the SDT variability. Using phase-differences from longitudinally separated meteor radars, we estimated the zonal wavenumber. Based on this analysis, we propose that nonlinear interaction between the quasi-16-day zonal wavenumber-2 planetary wave (Q16DW2) and the migrating semidiurnal tide (SW2) contributed to the observed longitudinal differences in SDT amplitude. Furthermore, nonlinear advection associated with Q16DW2-SDT interactions is examined and shows clear longitudinal differences that lead to longitudinal asymmetry in SDT amplitude. These findings show the strong modulation of the SDT by SH SSWs and underscore the combined roles of ozone variability and nonlinear wave interactions in modulating upper-atmospheric tidal responses.

This study provides a comprehensive description of the meteoric cycle on Venus, considering the temporal, latitudinal, and orbital variations of meteoroid mass influx before atmospheric entry, the ablation rates and the subsequent ionization of meteoric elements in the upper atmosphere, along with the accretion of micrometeorites at the surface. The study integrates three models: (i) the NASA-GSFC Meteoroid Input Function for Venus, which characterizes the size, velocity, and radiant distributions of the Jupiter-family comets (JFCs), main-belt asteroids, Halley-type comets (HTCs), and Oort-cloud comets (OCCs); (ii) the University of Leeds Chemical Ablation Model, which computes ablation rates of 12 meteoric species based on entry parameters; and (iii) the Electron Linear Density model, which estimates the ionization probabilities from hyperthermal collisions with atmospheric molecules. The total meteoroid mass influx is shown to peak during Venus’ ecliptic crossings (∼31.8 × 10 ^3 kg Earth-day ^−1 at the second crossing) and reaches a minimum around the minimum and maximum vertical displacements (∼24.2 × 10 ^3 kg Earth-day ^−1 ). The JFCs dominate pre-atmospheric mass input and largely drive variability along Venus’ orbit, while ablation is primarily contributed by the HTCs and OCCs. Ablation exhibits a pronounced diurnal asymmetry at equator, with enhanced injection on the dayside hemisphere around a height of 118 km. Neutral species account for 83.1% of ablated species, while ionization dominates above ∼119 km, particularly for Na and K. JFCs supply ∼90% of micrometeorites deposited at the surface, being the maximum accretion rates of organics at the second crossing between ∼0.3 × 10 ^3 kg Earth-day ^−1 (CI-chondrite) and ∼1.7 × 10 ^3 kg Earth-day ^−1 (cometary enrichment).

Vertical winds induced by the residual circulation are extremely challenging to retrieve from measurements. Multistatic meteor radar networks facilitate implementing more sophisticated tomographic wind retrievals, either based on Bayesian inversions such as the 3DVAR+DIV algorithm or the spherical volume velocity processing (SVVP). A vertical wind climatology obtained from the Nordic Meteor Radar Cluster (NORDIC) showed summer upwelling with vertical winds between 8-12 cm/s corresponding to a cooling rate of 80 K/d. During the winter season, the downwelling indicated values of -2 to -4 cm/s, resulting in a warming of 15-25 K/d. An analysis of the time series from 2022 to 2025 revealed a correlation between the vertical wind magnitude and the strength of the meridional wind during the summer months, as expected from the residual circulation. Furthermore, we compared winds observed with NORDIC to the meteorological reanalysis JAWARA.

Over 20,000 tons of microgram-scale meteoroids are estimated to enter Earth’s atmosphere annually. These particles, typically fragments from asteroids or comets, collide with neutral air molecules, heat, and ablate, resulting in a plasma commonly known as a shooting star, or meteor. Meteors form between $70-120 \mathrm{~km}$ altitude, travel at velocities between $11-72 \mathrm{~km} / \mathrm{s}$, and their brightness depends on both their mass and velocity. Meteor observations provide valuable insight into the physical properties of their parent bodies, their influence on the upper atmosphere, and potential hazards posed to spacecraft. Yet the atmospheric region itself is difficult to probe directly: it lies too high for weather balloons and too low for satellites. Optical instruments are limited to detecting larger meteoroids down to the milligram scale. Radar is the primary ground-based method for detecting and characterizing micrometeoroids, capturing reflections from the surrounding plasma cap, known as head echoes (HEs), as well as reflections from the trailing plasma, known as trail echoes (TEs). HEs are particularly valuable since they track the meteoroid directly, but their non-specular nature means they are best detected by high-power large aperture (HPLA) radars ($\gt1$ MW transmit power, $\sim 1^{\circ}$ HPBW) such as the Jicamarca Radio Observatory (JRO). However, HE detections have been demonstrated at non-HPLA facilities, including Southern Argentina Agile Meteor Radar (SAAMER).

Abstract. The Southern Argentina Agile MEteor Radar – Novel Atmospheric Sounding (SAAMER-NOVA) is the newest meteor radar network, an advancement to the SAAMER project, which has been operational since May 2008. The SAAMER-NOVA became fully operational in October 2025, using a monostatic meteor radar situated at Rio Grande (67.8° W, 53.8° S), alongside two passive receiver systems near the town of Tolhuin (67.1° W, 54.5° S) and the border crossing Radman (68.6° W, 54.0° S), south and west of Rio Grande, respectively. These remote receiver stations form an almost perfect rectangular triangle, which optimises measurement response, and the angular diversity permits analysis of small-scale divergent and vortical structures. This network successfully provides measurements with a default 15–30 min temporal resolution in the mesosphere and lower thermosphere (MLT). Daily meteor echoes detected at SAAMER-NOVA are approximately 20,639, with the highest counts at Tolhuin, followed by Radman and then Rio Grande. This extensive meteor detection permits the retrieval of spatially resolved, high-resolution three-dimensional wind fields from this network using sophisticated retrieval models such as 3DVAR+DIV, VVP, and SVVP. In this paper, we describe the statistics and cross-site validation of SAAMER-NOVA wind products spanning from October 2025 to January 2026 and 1st – 31st January 2026, respectively. We present snapshots of tomographic wind reconstructions retrieved from 3DVAR+DIV, Altitude-Time Wind (ATW) profiles, and zonal and meridional keograms of latitudinal and longitudinal cross-sections. The ATW Figures reveal diurnal variations and several wave activities across the region. The motivation for deploying the SAAMER-NOVA network at the southern tip of Argentina is to expand and enhance atmospheric measurements in a region recognised as a hotspot for atmospheric gravity wave (GW) activity. This strategic positioning at the southern tip of the Andes enables unique, advanced observations of MLT dynamics and the first imaging meteor radar network in Tierra del Fuego. The new SAAMER-NOVA capabilities provide a pathway to benchmark existing circulation models for small-scale GW dynamics over one of the world’s most significant GW source regions and to guide investigations into the multistep vertical coupling between atmospheric layers.

Abstract. Radar echoes from meteor plasma trails constitute one of the main sources of observations of winds in the mesosphere-lower thermosphere. A new 31-year archive of meteor wind observations has been prepared from data taken at 38 Super Dual Auroral Radar Network (SuperDARN) sites, covering 1993–2024. These observations are not height-resolved, and so an empirical meteor model has been produced to estimate the altitude contribution function, in other words the meteor count distribution. The meteor count model RMSEs were estimated at 1.1 km for the peak height and 1.0 km for the full width at half maximum. Using the meteor model, the SuperDARN wind observations have been compared against nearby dedicated meteor radar data, and against JAWARA reanalysis winds. Two case-study comparisons were performed: one for the Andenes meteor radar versus Hankasalmi SuperDARN radar in 2008, and one for the McMurdo meteor radar versus McMurdo SuperDARN radar in 2019. The three datasets were found to be in reasonable agreement, with correlations ranging from 0.49–0.88 for the comparison of SuperDARN against the meteor and 0.50 – 0.72 for the comparison of SuperDARN against JAWARA. A summertime equatorward mean flow of 5–15 m/s was identified in the northern hemisphere SuperDARN data, consistent with previous reports.

Abstract. Continuous measurements of vertical wind in the mesosphere and lower thermosphere are rare and technically challenging. However, multistatic meteor radar networks, such as the Nordic Meteor Radar Cluster, offer a unique opportunity to use advanced tomographic wind retrieval methods to determine neutral winds, including vertical wind components. The Spherical Volume Velocity Processing technique is a newly developed tomographic algorithm that enables the extraction of Doppler-based vertical winds and the computation of vertical winds from horizontal divergence through vertical integration.In this study, we present an intercomparison of various vertical wind retrieval methods to evaluate remaining biases and to quantify the magnitude of summer mesospheric vertical upwelling and corresponding downwelling. The retrieved wind data are compared with the Japanese meteorological reanalysis known as JAWARA, as well as a year of free-running SE-WACCM-X model data. Our findings indicate a strong agreement concerning the seasonal patterns of horizontal winds between the Nordic Meteor Radar Cluster and both models. The observed vertical wind velocities range from 2 to 15 cm/s. Additionally, measurements from the Nordic Meteor Radar Cluster show cooling and heating rates of -40 to 100 K/day during summer and 5 to 20 K/day in the winter months.

The study of mass flux from meteoroids is key to understanding their influence on Earth’s atmosphere. Radar measurements are one of the main techniques used to characterize the distribution of this mass flux. As meteoroids enter the atmosphere, they are subject to ablation, a process in which the material is eroded and vaporized. The hyperthermal collisions of ablated meteoric chemical compounds with air molecules generate plasma with free electrons that can be detected by radars. However, the physical mechanisms controlling ablation and electron production are still not fully understood, and additional experimental investigations are required to improve current models.

We find observational evidence for mountain waves (MWs) and secondary gravity waves (2GWs) in the OH*(3-1) layer above Tierra del Fuego, Argentina. On the night of 21-22 May 2018, the Advanced Mesospheric Temperature Mapper (AMTM) obtained temperatures at km. During the westerly phase of the semi-diurnal tide, arc-shaped quasi-stationary structures in temperature maps indicated MWs with horizontal wavelengths of 20-40 km. A co-located temperature measurement from the COmpact Rayleigh Autonomous Lidar (CORAL) confirmed quasi-stationary structures down to 15 km, also indicating MWs. Temperature profiles revealed a convectively unstable region within a MW phase front at 58-66 km-a sign of MW breaking, momentum deposition, local body forces, and generation of 2GWs. After a wind reversal in the mesosphere/lower thermosphere (MLT) observed by the Southern Argentina Agile Meteor Radar (SAAMER), a gravity wave propagated southeastward with an intrinsic phase speed . Using 1-D cross-wavelet analysis, we derived spectral properties of this fast wave and performed ray-tracing, using the Japanese Whole Atmosphere Reanalysis as background. The fast wave likely originated near 63 km above the Torres del Paine region, known for large-amplitude MWs. We conclude that tropospheric forcing excites MWs over Tierra del Fuego (observed) and over the Torres del Paine massif (not observed) km northwest. The latter MWs likely generate 2GWs upon breaking in the lower mesosphere, observed over Tierra del Fuego after a turning-level disappearance. A novel momentum-flux (MF) retrieval, based on co-located AMTM, CORAL, and SAAMER measurements, automatically identifies dominant wave features, incorporating measurement and OH*(3-1) layer variability to infer realistic MF uncertainties.

Abstract. A growing number of multistatic meteor radar networks are being established worldwide. The multistatic geometry with overlapping observation volumes of several meteor radars or passive receivers permits the inference of higher-order kinematic properties of the wind field or even the retrieval of arbitrary wind fields using tomographic algorithms. Furthermore, there is the long-standing question of the reliability of the vertical wind. In this study, we present a novel Volume Velocity Processing in spherical coordinates and perform an initial cross-comparison to previous implementations of the Volume Velocity Processing and the advanced 3DVAR+DIV retrieval. We performed a detailed climatological and multiyear comparison of mean winds, horizontal divergence, relative vorticity, stretching, and shearing deformation using observations of the Nordic Meteor Radar Cluster consisting of the meteor radars at Tromsø, Alta, Kiruna, and Sodankylä. Our results underscore that the spherical implementation of Volume Velocity Processing reduces/minimizes altitude-dependent biases caused by projection errors resulting from an incomplete representation of the observation geometry in the mean horizontal and vertical winds. All algorithms exhibit a very high correlation for the mean horizontal winds, but we found substantial differences in the vertical wind velocity and for the higher-order kinematic properties between the novel algorithm compared to previous versions of the Volume Velocity Processing. Furthermore, the novel algorithm reproduces a consistent seasonal pattern of the vertical velocity with upwelling during the hemispheric summer at the altitude of the zonal wind reversal and a corresponding but weaker downwelling during the winter months. The magnitudes of the vertical wind appear to be physically consistent with theoretically expected upward and downward motions and are in the order of a few cm/s. We also identified a scaling effect of the vertical wind in dependence on the temporal resolution and spatial averaging represented by a circle of influence in the new retrieval, which was confirmed by the measurement response of the 3DVAR+DIV retrieval. The most reliable vertical winds were obtained for a temporal resolution of 15–30 minutes and a spatial domain of about 200–250 km centered between all meteor radars of the Nordic Meteor Radar Cluster.

NASA’s Atmospheric Waves Experiment (AWE) mission is a Heliophysics Small Explorers Mission of Opportunity designed to investigate how terrestrial weather affects space weather, via small-scale atmospheric gravity waves (AGWs) produced in Earth’s atmosphere. Following its launch to the International Space Station (ISS) in November 2023, AWE began a 2-year mission to explore the global distribution of AGWs, study the processes controlling their propagation throughout the upper atmosphere, and estimate their impacts on the ionosphere – thermosphere – mesosphere (ITM) system. The AWE science instrument consists of the Advanced Mesospheric Temperature Mapper (AMTM) — a wide field-of-view Shortwave Infrared (SWIR) imager that quantifies gravity wave-induced temperature disturbances in the hydroxyl (OH) airglow layer, which lies near the mesopause at ~87 km altitude. The AMTM’s four identical telescopes make continuous nighttime observations of the P1(2) and P1(4) emission lines of the OH (3,1) band and the Q1(1) emission line in the OH (2,0) band, as well as the atmospheric background, from which the OH layer temperature is derived. AWE images are collected once per second, co-added, and processed into temperature swaths using correction algorithms derived from ground calibration test results. Global coverage of the OH layer is provided about every four days, which enables regional and seasonal studies, as well as characterization of AGW ‘hot spots.’ This paper will present an overview of the AWE mission and discuss initial science results.

Ground-based meteor radars detect the plasma streaks produced when meteoroids ablate in our atmosphere. However they are limited to detecting particles that produce a sufficient amount of plasma within the instrument’s field-of-view, and thus most of the meteoroid’s trajectory remains undetected. Previous work by Dawkins et al. (2023) and Stober et al. (2023) utilised new polarisation measurements made by the Southern Argentina Agile Meteor Radar Orbital System (SAAMER-OS, 53.8oS, 67.8oW, Janches et al., 2019), in conjunction with two state-of-the-art models, in order to determine the pre-atmosphere dynamical characteristics (mass, velocity) of the detected particles before they suffered any significant ablation or deceleration. Subsequent work has focused on automating this methodology, to allow us to determine the pre-atmosphere characteristics for all meteoric particles detected by SAAMER-OS. In this work we describe this background methodology and how it can be applied to different facets of atmospheric and astronomical research, including (1) how we can characterise the astronomical sources detected at SAAMER-OS through time (mass and velocities), (2) detections of new meteor showers, (3) to understand the mass distribution function of particles that enter the top of the atmosphere, and (4) variability of atmospheric neutral densities in the Earth’s upper atmosphere.

The mesosphere and lower thermosphere (MLT) comprise a highly variable region that forms the transition region between the middle and upper atmosphere. The variability of this region is driven by atmospheric waves transporting energy and momentum from the lower and middle atmosphere to MLT altitudes. These waves cover a wide range of temporal (minutes to days) and spatial (kilometers to planetary) scales. The upward propagation of atmospheric gravity waves and tides is one of the key processes at all latitudes that alters the state of the ionosphere–thermosphere system, and their vertical propagation depends crucially on the background mean winds. The TIMED Doppler Interferometer (TIDI) on board the Thermosphere-Ionosphere-Mesosphere-Energetics and Dynamics (TIMED) satellite observes neutral winds at the MLT using airglow emissions. We establish a TIDI mean wind climatology, compare our results with existing climatologies derived from local meteor radar observations, and discuss similarities and differences depending on local time and geographical latitude.

Planetary wave (PW) modulation of gravity wave (GW) dissipation has long been proposed as a source of longitudinal variability in the mesosphere and lower thermosphere. However, direct measurements of GW drag are rare. We identify 2‐day wave variations in GW momentum fluxes measured by the Southern Argentina Agile Meteor Radar (SAAMER) in Rio Grande, Tierra del Fuego, and a meteor radar at the Andes Lidar Observatory (ALO) in Cerro Pachon, Chile. Typical amplitudes range from 1 to 5 and are generally, though not always, out of phase with the horizontal wind consistent with wind‐induced dissipation of upward‐propagating GWs. The 2‐day wave‐modulated GW drag ranges between 20 and 140 m and can amplify, damp, and alter the phase of the 2‐day wave. These multiple relationships between the GW drag and the 2‐day wave suggest that in situ processes may influence GW drag, including secondary GWs excited from the breakdown of primary GW packets.

The Hunga Tonga-Hunga Ha‘apai (HTHH) volcanic eruption on 15th January 2022 was an unprecedented event and a unique opportunity to investigate volcanic-caused gravity waves (GW) and their global propagation. In this study, we have combined all the available meteor radar observations and data analysis to identify the HTHH GW in the observations. Our results are compared to model-based wind perturbations from HIAMCM of secondary waves that are forced by the GW model MESORAC using GOES-17 observations. Furthermore, we leverage the GW polarization relations to identify different wave features in the observations and perturbation runs with HIAMCM. There is a remarkable agreement in the observed phase speeds for the eastward and westward GW propagation between the observations and HIAMCM wind perturbations indicating that the mesospheric HTHH GW are explainable by secondary waves generated by breaking of the primary GWs from the eruption. We also shed some light on the importance of the quasi-2-day wave on the HTHH GW propagation.

On the night of 21/22 May 2018, clear-sky conditions enabled a 12-hour-long temperature measurement of the Advanced Mesospheric Temperature Mapper (AMTM) in the mesosphere-lower thermosphere (MLT) region over Río Grande, Argentina. Given a westerly forcing over Patagonia, we observe North-South-oriented phase lines in the AMTM temperature maps exclusively during the westerly phase of the semi-diurnal tide, indicating the deep propagation of mountain waves (MWs) with horizontal wavelengths between 20 km and 40 km. After a wind reversal in the MLT, we observe two large-scale gravity waves (GWs) propagating rapidly in a south-eastward direction. We use one- and two-dimensional wavelet analysis to characterize the observed GWs and find that their wavelengths and phase speeds are consistent with secondary GW theory. Ray tracing results suggest a possible source region for these 2GWs located north-westward, near the Chilean Torres del Paine region. In addition, co-located temperature and wind measurements from the Compact Rayleigh Autonomous Lidar (CORAL) and the Southern Argentine Agile Meteor Radar (SAAMER), in combination with a Monte Carlo approach, allow for the accurate determination of both the GW momentum flux and its uncertainty. Although we exclude a direct cause-and-effect relationship within our field of view, we find that, on average, the observed MWs carry momentum fluxes an order of magnitude larger than those of the 2GWs.

Multistatic meteor radar networks have become a valuable tool to study the spatial and temporal variability of mesosphere/lower thermosphere winds. Combined with advanced and tomographic analysis such as the 3DVAR+DIV or VVP algorithm it is possible to infer spectral information related to the horizontal wavelength and the temporal spectrum. Here we present a statistical analysis of almost 5 years of observations recorded with the Nordic Meteor Radar Cluster and CONDOR. Our initial results show a seasonal variability of the spectral slopes for different spatial scales indicating a reduced gravity wave activity during the spring for the Northern hemispheric data. Furthermore, we find a transition from a k-3 to a k-5/3 slope for spatial scales around 150 kilometers. Zonal wavelength spectra at CONDOR exhibit a less clear seasonal pattern compared to the Nordic Meteor Radar Cluster.

Meteoroids of sub-milligram sizes burn up high in the Earth's atmosphere and cause streaks of plasma trails detectable by meteor radars. The altitude at which these trails, or meteors, form depends on a number of factors including atmospheric density and the astronomical source populations from which these meteoroids originate. A previous study has shown that the altitude of these meteors is affected by long-term linear trends and the 11-year solar cycle related to changes in our atmosphere. In this work, we examine how shorter diurnal and seasonal variations in the altitude distribution of meteors are dependent on the geographical location at which the measurements are performed. We use meteoroid altitude data from 18 independent meteor radar stations at a broad range of latitudes and investigate whether there are local time (LT) and seasonal variations in the altitude of the peak meteor height, defined as the majority detection altitude of all meteors within a certain period, which differ from those expected purely from the variation in the visibility of their astronomical source. We find a consistent LT and seasonal response for the Northern Hemisphere locations regardless of latitude. However, the Southern Hemisphere locations exhibit much greater LT and seasonal variation. In particular, we find a complex response in the four stations located within the Southern Andes region, which indicates that the strong dynamical atmospheric activity, such as the gravity waves prevalent here, disrupts, and masks the seasonality and dependence on the astronomical sources.