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The Hunga Tonga–Hunga Ha′apai volcano erupted on 15 January 2022, launching Lamb waves and gravity waves into the atmosphere. In this study, we present results using 13 globally distributed meteor radars and identify the volcanogenic gravity waves in the mesospheric/lower thermospheric winds. Leveraging the High-Altitude Mechanistic general Circulation Model (HIAMCM), we compare the global propagation of these gravity waves. We observed an eastward-propagating gravity wave packet with an observed phase speed of 240 ± 5.7 m s -1 and a westward-propagating gravity wave with an observed phase speed of 166.5 ± 6.4 m s -1. We identified these waves in HIAMCM and obtained very good agreement of the observed phase speeds of 239.5 ± 4.3 and 162.2 ± 6.1 m s -1 for the eastward the westward waves, respectively. Considering that HIAMCM perturbations in the mesosphere/lower thermosphere were the result of the secondary waves generated by the dissipation of the primary gravity waves from the volcanic eruption, this affirms the importance of higher-order wave generation. Furthermore, based on meteor radar observations of the gravity wave propagation around the globe, we estimate the eruption time to be within 6 min of the nominal value of 15 January 2022 04:15 UTC, and we localized the volcanic eruption to be within 78 km relative to the World Geodetic System 84 coordinates of the volcano, confirming our estimates to be realistic. [ABSTRACT FROM AUTHOR]

The Hunga Tonga-Hunga Ha'apai volcano erupted on 15th January 2022, launching Lamb waves and gravity waves into the atmosphere. In this study, we present results using 13 globally distributed meteor radars and identify the volcanic-caused gravity waves in the mesospheric/lower thermospheric winds. Leveraging the High-Altitude Mechanistic General Circulation Model (HIAMCM), we compare the global propagation of these gravity waves. We observed an eastward propagating gravity wave packet with an observed phase speed of 240 ± 5 5.7 m/s and a westward propagating gravity wave with an observed phase speed of 166.5 ± 6.4 m/s. We identified these waves in the HIAMCM and obtained very good agreement of the observed phase speeds of 239.5 ± 4.3 m/s and 162.2 ± 6.1 m/s for the eastward and the westward waves, respectively. Considering that HIAMCM perturbations in the mesosphere/lower thermosphere were the result of the secondary waves generated by the dissipation of the primary gravity waves from the volcanic eruption affirms the importance of higher-order wave generation. Furthermore, based on meteor radar observations of the gravity wave propagation around the globe, we estimate the eruption time to be within 6 minutes of the nominal value of 15th January 2022 04:15 UTC and localized the volcanic eruption to be within 78 km relative to the World Geodetic System 84 coordinates of the volcano confirming our estimates to be realistic. [ABSTRACT FROM AUTHOR]

Atmospheric Gravity Waves and Traveling Ionospheric Disturbances can be observed in the neutral atmosphere and the ionosphere at a wide range of spatial and temporal scales. Especially at medium scales, these oscillations are often not resolved in general circulation models and are parameterized. We show that ionospheric disturbances forced by upward propagating atmospheric gravity waves can be simultaneously observed with the EISCAT Very High Frequency incoherent scatter radar and the Nordic Meteor Radar Cluster. From combined multi-static measurements, both vertical and horizontal wave parameters can be determined by applying a specially developed Fourier filter analysis method. This method is demonstrated using the example of a strongly pronounced wave mode that occurred during the EISCAT experiment on 7 July 2020. Leveraging the developed technique, we show that the wave characteristics of Traveling Ionospheric Disturbances are notably impacted by the fall transition of the mesosphere/lower thermosphere. We also demonstrate the application of using the determined wave parameters to infer the thermospheric neutral wind velocities. Applying the dissipative anelastic gravity wave dispersion relation, we obtain vertical wind profiles in the lower thermosphere. [ABSTRACT FROM AUTHOR]

Atmospheric gravity waves and traveling ionospheric disturbances can be observed in the neutral atmosphere and the ionosphere at a wide range of spatial and temporal scales. Especially at medium scales, these oscillations are often not resolved in general circulation models and are parameterized. We show that ionospheric disturbances forced by upward-propagating atmospheric gravity waves can be simultaneously observed with the EISCAT very high frequency incoherent scatter radar and the Nordic Meteor Radar Cluster. From combined multi-static measurements, both vertical and horizontal wave parameters can be determined by applying a specially developed Fourier filter analysis method. This method is demonstrated using the example of a strongly pronounced wave mode that occurred during the EISCAT experiment on 7 July 2020. Leveraging the developed technique, we show that the wave characteristics of traveling ionospheric disturbances are notably impacted by the fall transition of the mesosphere and lower thermosphere. We also demonstrate the application of using the determined wave parameters to infer the thermospheric neutral wind velocities. Applying the dissipative anelastic gravity wave dispersion relation, we obtain vertical wind profiles in the lower thermosphere. [ABSTRACT FROM AUTHOR]

The Hunga Tonga–Hunga Ha′apai volcano eruption was a unique event that caused many atmospheric phenomena around the globe. In this study, we investigate the atmospheric gravity waves in the mesosphere/lower-thermosphere (MLT) launched by the volcanic explosion in the Pacific, leveraging multistatic meteor radar observations from the Chilean Observation Network De Meteor Radars (CONDOR) and the Nordic Meteor Radar Cluster in Fennoscandia. MLT winds are computed using a recently developed 3DVAR+DIV algorithm. We found eastward- and westward-traveling gravity waves in the CONDOR zonal and meridional wind measurements, which arrived 12 and 48 h after the eruption, and we found one in the Nordic Meteor Radar Cluster that arrived 27.5 h after the volcanic detonation. We obtained observed phase speeds for the eastward great circle path at both locations of about 250 m s -1 , and they were 170–150 m s -1 for the opposite propagation direction. The intrinsic phase speed was estimated to be 200–212 m s -1. Furthermore, we identified a potential lamb wave signature in the MLT winds using 5 min resolved 3DVAR+DIV retrievals. [ABSTRACT FROM AUTHOR]

Ground-based remote sensing of atmospheric parameters is often limited to single station observations by vertical profiles at a certain geographic location. This is a limiting factor for investigating gravity wave dynamics as the spatial information is often missing, e.g., horizontal wavelength, propagation direction or intrinsic frequency. In this study, we present a new retrieval algorithm for multistatic meteor radar networks to obtain tomographic 3-D wind fields within a pre-defined domain area. The algorithm is part of the Agile Software for Gravity wAve Regional Dynamics (ASGARD) and called 3D-Var, and based on the optimal estimation technique and Bayesian statistics. The performance of the 3D-Var retrieval is demonstrated using two meteor radar networks: the Nordic Meteor Radar Cluster and the Chilean Observation Network De Meteor Radars (CONDOR). The optimal estimation implementation provide statistically sound solutions and diagnostics from the averaging kernels and measurement response. We present initial scientific results such as body forces of breaking gravity waves leading to two counter-rotating vortices and horizontal wavelength spectra indicating a transition between the rotational k-3 and divergent k-5/3 mode at scales of 80–120 km. In addition, we performed a keogram analysis over extended periods to reflect the latitudinal and temporal impact of a minor sudden stratospheric warming in December 2019. Finally, we demonstrate the applicability of the 3D-Var algorithm to perform large-scale retrievals to derive meteorological wind maps covering a latitude region from Svalbard, north of the European Arctic mainland, to central Norway. [ABSTRACT FROM AUTHOR]

Ground-based remote sensing of atmospheric parameters is often limited to single station observations of vertical profiles at a certain geographic location. This can be a limiting factor to investigating gravity wave dynamics. In this study we present a new retrieval algorithm for multi-static meteor radar networks to obtain tomographic 3D wind fields within a pre-defined domain area. The algorithm is part of the Agile Software for Gravity wAve Regional Dynamics (ASGARD) called 3DVAR, and based on the optimal estimation technique and Bayesian statistics. The performance of the 3DVAR retrieval is demonstrated using two meteor radar networks, the Nordic Meteor Radar Cluster and the Chilean Observation Network De MeteOr Radars (CONDOR). The optimal estimation implementation provides a statistically sound solution and additional diagnostics from the averaging kernels and measurement response. We present initial scientific results such as body forces of breaking gravity waves leading to two counter-rotating vortices and horizontal wavelength spectra indicating a transition between the vortical κ-3 and divergent κ-5/3 mode at scales of 80-120 km. In addition, we have performed a keogram analysis over extended periods to reflect the latitudinal and temporal impact of a minor sudden stratospheric warming in December 2019. Finally, we demonstrate the applicability of the 3DVAR algorithm to perform large-scale retrievals to derive meteorological wind maps covering a latitude region from Svalbard, north of the European Arctic mainland, to mid-Norway. [ABSTRACT FROM AUTHOR]

We analyse gravity waves in the upper-mesosphere, lower-thermosphere region from high-resolution temperature variations measured by the Rayleigh lidar and OH temperature mapper. From this combination of instruments, aided by meteor radar wind data, the full set of ground-relative and intrinsic gravity wave parameters are derived by means of the novel WAPITI (Wavelet Analysis and Phase line IdenTIfication) method. This WAPITI tool decomposes the gravity wave field into its spectral component while preserving the temporal resolution, allowing us to identify and study the evolution of gravity wave packets in the varying backgrounds. We describe WAPITI and demonstrate its capabilities for the large-amplitude gravity wave event on 16–17 December 2015 observed at Sodankylä, Finland, during the GW-LCYCLE-II (Gravity Wave Life Cycle Experiment) field campaign. We present horizontal and vertical wavelengths, phase velocities, propagation directions and intrinsic periods including uncertainties. The results are discussed for three main spectral regions, representing small-, medium- and large-period gravity waves. We observe a complex superposition of gravity waves at different scales, partly generated by gravity wave breaking, evolving in accordance with a vertically and presumably also horizontally sheared wind. [ABSTRACT FROM AUTHOR]

Wind and temperature in the polar mesosphere-lower thermosphere (MLT) region are observed by the Sodankyla meteor radar, which is located in the vicinity of the southern edge of the stratospheric polar vortex and also close to the equatorial boundary of the auroral oval in the ionosphere. At 90 km height, the seasonal pattern is formed by the cold summer (100 К) and warm winter (200 К). The mean zonal winds are characterized with summer westward flow of about 30 m/s at 80-90 km heights and the eastward flow above 90 km. In winter the flow is eastward at all heights. The meridional winds are dominated by winter poleward flow and summer equatorward flow, with a jet core of about 15 m/s located slightly below 90 km. The structure observed corresponds to the polar branch of the seasonal inter-hemispheric circulation. The systematically varying winds are mostly the semidiurnal tides up to 40 m/s. Under conditions of low solar activity, pronounced sudden mesospheric cooling linked to major stratospheric warming (SSW) is observed, while no SSW-related thermal signatures are detected in the mesosphere during the solar maximum years. The mesospheric temperature minimum occurs 1 day ahead of the SSW maximum, and the cooling is almost of the same magnitude as the corresponding warming (~50 K). The reversal of mesospheric wind is also observed.A rapid-run ionosonde continuously operates at the same site since 2007. Quasi periodic oscillations of the F-layer height with a period from several minutes to hours which are related to the travelling ionospheric disturbances caused by atmospheric gravity waves (AGW) are revealed. Long term variations of the AGW amplitudes depend on seaon, solar and geomagnetic activity. At the shorter time scales, wave penetration to the ionospheric heights is affected by the underlying atmosphere. While the mesospheric temperature reaches its minimum in the course of SSW, the amplitude of ionospheric AGW with periods of 10–60 min decay abruptly. The longer period waves are not affected. The effect is explained by selective filtering and increased atmospheric turbulence near the mesopause thermal inversion layer. [ABSTRACT FROM AUTHOR]

The characterization of gravity waves is one of the crucial elements for understanding middle atmospheric dynamics. Although advanced models exist, linear wave theory is still an attractive option as the first step towards data interpretation due to its simplicity. In this paper, we will review some common literature, and attempt to bring clarity into the nomenclature of wave frequencies in different frames of reference. We specifically relate the speed of the obstacle that act as a source to the phase speed of the excited wave. Using linear wave theory under steady horizontally uniform background conditions, a framework is established to re-interpret the wave pattern that has been previously recorded by lidar in Dörnbrack et al. (2017). The event can be explained by a simple quasi-monochromatic wave influenced by the change in the shear of mean wind, instead of an interaction between wave packets as has previously been suggested. The results are then compared to realistic wind data to confirm that the mean wind condition has indeed changed dramatically and that the assumed source speed around 60 m/s is a sound estimate. Furthermore, the wave possibly has traveled towards south south east direction. [ABSTRACT FROM AUTHOR]