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  • 1
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    Horizontal Wavenumber Spectra of Vertical Vorticity and Horizontal Divergence of Mesoscale Dynamics in the Mesosphere and Lower Thermosphere Using Multistatic Specular Meteor Radar Observations (2022)
    Details
    Publication Date: 2023-01-14
    Description: Specular meteor radars (SMRs) have significantly contributed to the understanding of wind dynamics in the mesosphere and lower thermosphere (MLT). We present a method to estimate horizontal correlations of vertical vorticity (Qzz) and horizontal divergence (P) in the MLT, using line‐of‐sight multistatic SMRs velocities, that consists of three steps. First, we estimate 2D, zonal, and meridional correlation functions of wind fluctuations (with periods less than 4 hr and vertical wavelengths smaller than 4 km) using the wind field correlation function inversion (WCFI) technique. Then, the WCFI's statistical estimates are converted into longitudinal and transverse components. The conversion relation is obtained by considering the rotation about the vertical direction of two velocity vectors, from an east‐north‐up system to a meteor‐pair‐dependent cylindrical system. Finally, following a procedure previously applied in the upper troposphere and lower stratosphere to airborne wind measurements, the longitudinal and transverse spatial correlations are fitted, from which Qzz, P, and their spectra are directly estimated. The method is applied to a special Spread spectrum Interferometric Multistatic meteor radar Observing Network data set, obtained over northern Germany for seven days in November 2018. The results show that in a quasi‐axisymmetric scenario, P was more than five times larger than Qzz for the horizontal wavelengths range given by ∼50–400 km, indicating a predominance of internal gravity waves over vortical modes of motion as a possible explanation for the MLT mesoscale dynamics during this campaign.
    Description: Key Points: We investigate the horizontal correlation functions of vertical vorticity and horizontal divergence for mesoscale wind fluctuations in the mesosphere and lower thermosphere. 2D zonal and meridional correlation functions and 1D longitudinal and transverse correlation functions as a function of horizontal lags are analyzed. The divergence dominated over the vorticity during November 2018 in northern Germany.
    Description: Leibniz SAW
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: French Ministry of Foreign and European
    Description: https://doi.org/10.22000/536
    Keywords: ddc:551.5 ; MLT ; vorticity ; correlation function ; meteor radar ; mesoscales ; divergence
    Language: English
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  • 2
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    Horizontal Correlation Functions of Wind Fluctuations in the Mesosphere and Lower Thermosphere (2023)
    Details
    Publication Date: 2023-06-21
    Description: Measurements of kinetic energy in vortical and divergent fluctuations in the mesosphere and lower thermosphere can be used to study stratified turbulence (ST) and gravity waves. This can be done using horizontal correlation functions of the fluctuating component of velocity. This study introduces a novel method for estimating these correlation functions using radars that observe Doppler shifts of ionized specular meteor trails. The technique solves the correlation functions directly on a longitudinal‐transverse‐up coordinate system, assuming axial symmetry. This procedure is more efficient and leads to smaller uncertainties than a previous approach. The new technique is applied to a year‐long data set from a multistatic specular meteor radar network in Germany, to study the annual variability of kinetic energy within turbulent fluctuations at 87–93 km of altitude. In monthly averages, the kinetic energy is found to be nearly equipartitioned between vortical and divergent modes. Turbulent fluctuations maximize during the winter months with approximately 25% more energy in these months than at other times. The horizontal correlation functions are in agreement with the inertial subrange of ST, exhibiting a 2/3 power law in the horizontal lag direction, with an outermost scale of ST to be about 380 km. This suggests that horizontal correlation functions could be used to estimate turbulent energy transfer rates.
    Description: Plain Language Summary: Flows exhibit a phenomenon called turbulence, which transfers energy from large scales into smaller scales. This effect is important to quantify the energy budget of the Earth's upper atmosphere. The range of length scales where this phenomenon occurs is called the inertial subrange of turbulence. The classical theory of isotropic turbulence predicts that this energy transfer occurs on length scales smaller than ∼100 m, at 60–110 km altitude. Recent work has shown that horizontal velocity fluctuations can extend the inertial subrange to length scales of up to hundreds of kilometers horizontally. This type of turbulence is called stratified turbulence (ST). So far no comprehensive study has been made to experimentally examine ST in the mesosphere and lower thermosphere (MLT) region on horizontal mesoscales. This study introduces a method for doing so by measuring how the wind fluctuations are correlated as a function of horizontal separation. This is achieved by using meteor radar measurements. The technique is applied to a year‐long data set over Germany. It is found that the MLT wind fluctuations are compatible with ST theory. The introduced method could potentially be used for routinely measuring how kinetic energy flows from large‐scale to small‐scale atmospheric fluctuations.
    Description: Key Points: A more efficient estimator for horizontal correlation functions is introduced. The rotational and divergent correlation functions of mesosphere and lower thermosphere wind fluctuations are found to be balanced at horizontal mesoscales. Horizontal correlations of wind fluctuations follow a 2/3‐power law for horizontal separations of up to 300–400 km.
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: French Ministry of Foreign and European Affairs
    Description: Leibniz SAW project FORMOSA
    Keywords: ddc:551.5 ; mesosphere ; lower thermosphere ; wind fluctuations
    Language: English
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  • 3
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    Investigation of a Dissipating Mesospheric Bore Using Airglow Imager and Direct Numerical Simulation (2023)
    Details
    Publication Date: 2023-10-26
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Atmospheric gravity waves play an important role in driving the dynamics of the Mesosphere and Lower Thermosphere and the basic structure of this region is determined by momentum deposition of these waves. Mesospheric bores are a type of non‐linear response that cause the amplification of gravity wave, due to trapping, that is characterized by a propagating step‐like jump followed by undulating waves. They require a stable layer or duct to travel horizontally with little attenuation thereby capable of transporting wave energy and momentum over larger distances. We present a prominent bright undular bore event observed in the mesospheric O(〈sup〉1〈/sup〉S), O〈sub〉2〈/sub〉, and OH emission layers on 16 March 2021 over Germany. A striking feature of this observation is the capture of bore's rapid dissipation around the center of the imager's field of view. The vertical temperature profile obtained from the satellite data indicates the presence of temperature inversion layer which acted as a thermal duct for the bore propagation. In addition, we have performed idealized two dimensional direct numerical simulations (DNS) of Navier‐Stokes equations under Boussinesq approximation. The DNS results reproduce many important characteristics of the observed airglow event like the nonlinear wave‐steepening, number of trailing waves, and its dissipation by implementing a thermal duct and a wave‐like perturbation. Furthermore, the DNS results also indicate that the duct width and amplitude of the initial perturbation have a considerable effect on the bore morphology.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Observation of a mesospheric bright bore event that dissipated within the field of view〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉The duct that enabled the bore propagation was near the O(〈sup〉1〈/sup〉S) emission layer based on the observational data〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉The majority of the observed features are reproduced with idealized 2D direct numerical simulations using Boussinesq approximation〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Alexander von Humboldt‐Stiftung http://dx.doi.org/10.13039/100005156
    Description: https://doi.org/10.22000/809
    Description: http://sirius.bu.edu/data/
    Description: http://saber.gats-inc.com/coin.php
    Keywords: ddc:551.5 ; bores ; direct numerical simulations ; gravity waves ; inversion layers
    Language: English
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  • 4
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    Momentum Flux and Vertical Wind Power Spectral Characteristics in the Troposphere and Lower Stratosphere Over Andøya, Norway as Observed by MAARSY (2023)
    Details
    Publication Date: 2023-07-21
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉We used the tropospheric and lower stratospheric 3D winds for four consecutive years (2017–2020) to study the momentum flux (MF) and vertical wind power spectra (VWP) over Andøya, Norway (69.30°N, 16.04°E) using the Middle Atmosphere Alomar Radar System. The spectra range from 3.5 days〈sup〉−1〈/sup〉 > 〈italic〉f〈/italic〉 > 30 min〈sup〉−1〈/sup〉, which are categorized in terms of observed/ground‐based frequency (as the local inertial period is 13 h over Andøya), height ranges, and seasons. Our results indicate for the first time that (a) both the zonal and meridional MF display peaks around the inertial period (13 h) in the troposphere (1.80–12.00 km) during all seasons (with some exceptions), while VWP exhibits such features in the whole height range (1.80–18.00 km), (b) the minimum variability in MF, VWP, and kinetic energy is observed during summer, and (c) both the MF and VWP demonstrate height variation with maximum deviations below the tropopause.〈/p〉
    Description: Plain Language Summary: The wind measurements are used to study the height and seasonal variation of momentum flux and vertical wind power spectra during 2017–2020. We report for the first time that both the momentum flux and vertical wind power spectra depict more variations in the tropospheric heights (around 1.80–7.20 km), below the tropopause, with the minimum amplitudes in the summer months (June–July–August). Moreover, long‐period oscillations have more energy than short‐period oscillations, and therefore, contribute more to the energy or flux transfer from the lower to the higher atmosphere. The month versus height profile of kinetic energy also portrays a similar feature with considerably more magnitude for the long‐period oscillations than the short‐period ones. The kinetic energy displays an enhancement of magnitude near the tropopause (∼5.00–10.00 km).〈/p〉
    Description: Key Points: The zonal and meridional momentum flux spectra exhibit a peak around the inertial period of 13 h in the troposphere (1.80–12.00 km). Height profiles of momentum flux, vertical wind power spectra, and kinetic energy display seasonal variation with a minimum during summer. The maximum variability of momentum flux and vertical wind power spectra is noticed below tropopause and decreases with increasing height.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: https://doi.org/10.22000/766
    Keywords: ddc:551.5 ; atmospheric gravity waves ; momentum flux ; power spectra ; kinetic energy
    Language: English
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  • 5
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    Extreme Horizontal Wind Perturbations in the Mesosphere and Lower Thermosphere Over South America Associated With the 2022 Hunga Eruption (2023)
    Details
    Publication Date: 2024-04-03
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉On 15 January 2022, the Hunga volcano produced a massive explosion that generated perturbations in the entire atmosphere. Nonetheless, signatures in the mesosphere and lower thermosphere (MLT) have been challenging to identify. We report MLT horizontal wind perturbations using three multistatic specular meteor radars on the west side of South America (spanning more than 3,000 km). The most notorious signal is 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. Using a customized analysis, the wave is characterized as traveling at ∼200 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 〈italic〉L〈/italic〉〈sub〉1〈/sub〉 Lamb wave mode. The signal's timing coincides with the arrival time of the tsunami triggered by the eruption.〈/p〉
    Description: Plain Language Summary: The eruption of the Hunga volcano in January 2022 had a widespread impact on the atmosphere, affecting various layers. We describe a perturbation in horizontal winds caused by the event, which was observed over the west coast of South America by three different meteor radar systems separated by more than 3,000 km between them. The perturbation behaved similarly in the altitude range of 80–100 km, and the wave parameters observed were consistent with high‐order Lamb wave solutions from simulations carried out using the Whole Atmosphere Community Climate Model with thermosphere/ionosphere extension. This finding complements other studies that have explored the impacts of the eruption on different atmospheric levels. Overall, this study provides valuable insights into the complex and far‐reaching effects of volcanic eruptions on the atmosphere.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Hunga eruption generated extreme horizontal wind perturbations at 80–100 km of altitude over South America〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉The signal was detected almost simultaneously by three multistatic meteor radar systems spanning more than 3,000 km〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉The perturbation had a period of ∼2 hr, a horizontal phase velocity of ∼200 m/s, and a horizontal wavelength of ∼1,440 km〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Leibniz SAW project FORMOSA
    Description: https://doi.org/10.22000/956
    Keywords: ddc:551.5 ; South America ; 2022 Hunga Eruption ; mesosphere ; lower thermosphere ; horizontal wind perturbations
    Language: English
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  • 6
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    Quasi‐10‐Day Wave and Semidiurnal Tide Nonlinear Interactions During the Southern Hemispheric SSW 2019 Observed in the Northern Hemispheric Mesosphere (2021)
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    Publication Date: 2021-07-04
    Description: Mesospheric winds from three longitudinal sectors at 65°N and 54°N latitude are combined to diagnose the zonal wave numbers (m) of spectral wave signatures during the Southern Hemisphere sudden stratospheric warming (SSW) 2019. Diagnosed are quasi‐10‐ and 6‐day planetary waves (Q10DW and Q6DW, m = 1), solar semidiurnal tides with m = 1, 2, 3 (SW1, SW2, and SW3), lunar semidiurnal tide, and the upper and lower sidebands (USB and LSB, m = 1 and 3) of Q10DW‐SW2 nonlinear interactions. We further present 7‐year composite analyses to distinguish SSW effects from climatological features. Before (after) the SSW onset, LSB (USB) enhances, accompanied by the enhancing (fading) Q10DW, and a weakening of climatological SW2 maximum. These behaviors are explained in terms of Manley‐Rowe relation, that is, the energy goes first from SW2 to Q10DW and LSB, and then from SW2 and Q10DW to USB. Our results illustrate that the interactions can explain most wind variabilities associated with the SSW.
    Description: Plain Language Summary: Sudden stratospheric warming events occur typically over the winter Arctic and are well known for being accompanied by various tides and Rossby waves. A rare SSW occurred in the Southern Hemisphere in September 2019. Here, we combine mesospheric observations from the Northern Hemisphere to study the wave activities before and during the warming event. A dual‐station approach is implemented on high‐frequency‐resolved spectral peaks to diagnose the horizontal scales of the dominant waves. Diagnosed are multiple tidal components, multiple Rossby normal modes, and two secondary waves arising from nonlinear interactions between a tide component and a Rossby wave. Most of these waves do not occur in a climatological sense and occur around the warming onset. Furthermore, the evolution of these waves can be explained using theoretical energy arguments.
    Description: Key Points: Mesospheric winds from multiple longitudes in the NH are combined to diagnose zonal wave numbers of waves during the Antarctic SSW 2019. Diagnosed are Q6DW, Q10DW, M2, SW1, SW2, SW3, and LSB and USB of Q10DW‐SW2 nonlinear interactions. LSB and USB are generated asynchronously, during which their parent waves evolve following the Manley‐Rowe energy relations.
    Description: National Natural Science Foundation of China (NSFC) http://dx.doi.org/10.13039/501100001809
    Description: National Science Foundation (NSF) http://dx.doi.org/10.13039/100000001
    Description: German Research Foundation (DFG)
    Keywords: 551.5 ; sudden stratospheric warming (SSW) ; semidiurnal tides ; nonlinear interactions ; quasi‐10‐day wave ; quasi‐6‐day wave ; Manley‐Rowe relation
    Type: article
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  • 7
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    First Studies of Mesosphere and Lower Thermosphere Dynamics Using a Multistatic Specular Meteor Radar Network Over Southern Patagonia (2021)
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    Publication Date: 2021-07-21
    Description: This paper presents for the first time results on winds, tides, gradients of horizontal winds, and momentum fluxes at mesosphere and lower thermosphere altitudes over southern Patagonia, one of the most dynamically active regions in the world. For this purpose, measurements provided by SIMONe Argentina are investigated. SIMONe Argentina is a novel multistatic specular meteor radar system that implements a Spread‐spectrum Interferometric Multistatic meteor radar Observing Network (SIMONe) approach, and that has been operating since the end of September 2019. Average counts of more than 30,000 meteor detections per day result in tidal estimates with statistical uncertainties of less than 1 m/s. Thanks to the multistatic configuration, horizontal and vertical gradients of the horizontal winds are obtained, as well as vertical winds free from horizontal divergence contamination. The vertical gradients of both zonal and meridional winds exhibit strong tidal signatures. Mean momentum fluxes are estimated after removing the effects of mean winds using a 4‐h, 8‐km window in time and altitude, respectively. Reasonable statistical uncertainties of the momentum fluxes are obtained after applying a 28‐day averaging. Therefore, the momentum flux estimates presented in this paper represent monthly mean values of waves with periods of 4 h or less, vertical wavelengths shorter than 8 km, and horizontal scales less than 400 km.
    Description: Key Points: First observations of mesosphere and lower thermosphere dynamics over one of the most dynamically active regions in the world Estimates of mean horizontal winds and their gradients are possible, thanks to the multistatic configuration Mean momentum fluxes are estimated with vertical velocity estimates free of horizontal divergence contamination
    Description: Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659
    Description: Bundesministerium für Bildung und Forschung (BMBF) http://dx.doi.org/10.13039/501100002347
    Keywords: 551.5 ; horizontal gradients ; meteor radar ; MLT ; momentum flux ; tides ; winds
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  • 8
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    DFG priority programme 1788 „Dynamic Earth“: A joint interpretation of geomagnetic, geodetic and ionosphere/thermosphere data from low-orbit satellite missions (2021)
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    Publication Date: 2022-12-01
    Description: Deutsche Forschungsgemeinschaft
    Description: poster
    Keywords: ddc:550
    Language: English
    Type: doc-type:conferenceObject
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  • 9
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    Complex Plane Specular Meteor Radar Interferometry (2018)
    American Geophysical Union
    Details
    Publication Date: 2018-01-01
    Print ISSN: 0048-6604
    Electronic ISSN: 1944-799X
    Topics: Geosciences , Physics
    Published by American Geophysical Union
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  • 10
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    Relations Between Semidiurnal Tidal Variants Through Diagnosing the Zonal Wavenumber Using a Phase Differencing Technique Based on Two Ground-Based Detectors (2018)
    American Geophysical Union
    Details
    Publication Date: 2018-04-26
    Description: The winter upper atmosphere is associated with semidiurnal tidal variants, referring collectively to enhancements of near-12 h periodicities, including the lunar tide-like (M2) periodicity, solar semidiurnal (S2) spectral sidebands, and the quasi-semidiurnal westward propagating modes with zonal wavenumbers m = 1 and 3 (qSW1 and qSW3). Here we formulate a multipoint technique and implement the technique for a configuration of two midlatitude meteor radars, from Germany and China, to investigate the tidal variants. Statistical results illustrate that the 12 h periodicity is dominated consistently by the expected migrating mode (m = 2) between 2012 and 2016, consistent with the tidal climatology and in turn validating the technique. Our case study of 2013 sudden stratospheric warming reveals that the 11.6 h periodicity is characterized by m = 3, whereas the 12.4 h periodicity is dominated by m = 2 mode with a maximum amplitude 7.5 m/s and also comprises an additional mode m = 1 with a maximum amplitude 3.3 m/s. These observational evidences demonstrate, explicitly and for the first time, that (1) two independently reported categories of the variants, namely, the sidebands and the qSW1/qSW3 enhancements, are two different perspectives of identical phenomena, namely, the secondary waves of nonlinear interactions between SW2 and planetary waves, and (2) while M2 and the qSW1-associated secondary wave are entangled in the 12.4 h periodicity, M2 is superior to the sideband. ©2018. American Geophysical Union. All Rights Reserved.
    Print ISSN: 2169-897X
    Electronic ISSN: 2169-8996
    Topics: Geosciences , Physics
    Published by American Geophysical Union
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