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  • 1
    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
    Type: doc-type:article
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  • 2
    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
    Type: doc-type:article
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  • 3
    Publication Date: 2024-01-22
    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"〉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 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 plays a role in the mesopause region during summer.〈/p〉
    Description: Plain Language Summary: 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. 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 consider the theory of layered anisotropic stratified turbulence to study the summer mesopause region and hypothesize that this type of turbulence (in the statistical sense) plays a role in the transition of internal gravity waves to small‐scale turbulence.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Spatially filtered horizontal wind residuals are explored for the first time at mesopause altitudes over Patagonia〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Frequency spectra of horizontal wind residuals follow a −2 slope〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Simulated divergent and rotational parts of the mesoscale kinetic energy are equipartitioned at high frequencies〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: Leibniz Society
    Description: https://doi.org/10.22000/1737
    Keywords: ddc:551.5 ; stratified turbulence ; gravity waves ; mesopause ; meteor radar ; energy spectrum
    Language: English
    Type: doc-type:article
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  • 4
    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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  • 5
    Publication Date: 2022-08-16
    Description: Simultaneous observations from a 630 nm all-sky airglow imager, GNSS-TEC receivers, and an ionosonde are used to investigate the role of E- and F-region coupling on the generation of medium-scale traveling ionospheric disturbances (MSTIDs). The primary observations are OI 630 nm airglow images taken by an all-sky imager in Kühlungsborn (54.07°N; 11.46°E, 53.79°N Mlat.), a site in northern Germany. Out of 226 nights of observations, MSTIDs were found only in 18 nights, demonstrating the low occurrence rate over Kühlungsborn. We focused on four MSTIDs events: two during the vernal equinox and two during summer. Coincident measurements of detrended GNSS-TEC supported the presence of MSTIDs during the selected events, and simultaneous observations from the ionosonde in Juliusruh (54.60°N, 13.4°E, 54.02°N Mlat.) showed sporadic-E (Es) layer and spread-F activity in the E- and F-region, respectively. We observed the onset of the observed MSTIDs to be around the 15°–20°E longitude and 60–45°N latitude belts. Additionally, we found that in each case, the onset of MSTIDs coincides with the presence of an Es layer with sporadic-E trace is observed (foEs) exceeding 4 MHz. This suggests that an Es layer with foEs ≥ 4MHz was a source of the generation of these MSTIDs. Altitude of the Es layer could be another important factor in generating MSTIDs. The Es layer should exist at an altitude where Hall conductivity is large, as happened in the present study.
    Language: English
    Type: info:eu-repo/semantics/article
    Format: application/pdf
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  • 6
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    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Publication Date: 2023-05-03
    Description: One year of Spread spectrum Interferometric Multistatic meteor radar Observing Network (SIMONe) measurements are analyzed and compared for the first time between two low-latitude locations in Peru: Jicamarca (12°S, 77°W) and Piura (5°S, 80°W). Investigation of 28-day median values of the 4-hour, 4-km vertical momentum fluxes reveals that the mesosphere and lower thermosphere (MLT) mesoscale dynamics differ significantly between these two locations. From middle of July until October of 2021, a strong acceleration of the background zonal wind by westward-propagating gravity waves (GWs) is observed above ~90 km at both locations, although with larger amplitudes over Jicamarca. From middle of January until May of 2022, a second strong acceleration of the background zonal wind, again by westward-propagating GWs, is observed, but this time with larger amplitudes over Piura. These results observationally confirm the previous studies based on model simulations indicating that the directions of the GW drag and the background wind coincide in the low-latitude MLT [Yiğit & Medvedev, 2017]. Weak correlations between the horizontal wind gradients over Jicamarca and Piura reinforce the fact that the mesoscale dynamics are different at these two locations.
    Language: English
    Type: info:eu-repo/semantics/conferenceObject
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  • 7
    Publication Date: 2023-05-03
    Description: This work focuses on the annual characterization of the horizontal mean winds, tides (8, 12 and 24 hours) and quasi-two-day waves (Q2DWs) estimated at heights between 80-100 km over six latitudes in South and Central America (Costar Rica 9〈sup〉o〈/sup〉N, SIMONe Piura 5°S, SIMONe Jicamarca 12°S, CONDOR 30°S, SIMONe Argentina 50°S, and MMARIA-SAAMER 54°S). The main results are divided between low latitudes (+/-20°) and middle latitudes (above 20°). Based on these observations, in general, the zonal background winds show a semi-annual behavior at low latitudes (below 90 km) and quasi-annual behavior at middle latitudes, while the mean meridional wind shows a quasi-annual behavior for all latitudes. The main peak of the Q2DW occurs in January at all latitudes and a second peak is also present at low latitudes in March-April. Moreover, the Q2DW amplitudes are stronger at low latitudes and decrease as the latitude increases. Amplitudes of 24h tide are stronger at latitudes less than 30〈sup〉o〈/sup〉S; for higher latitudes they are weak. The maximum diurnal amplitudes occur in August-September and February-May in the southern hemisphere; and in December-April and July-August for Costa Rica, and its maximum value is reached by the meridional component over Costa Rica. Comparisons with general circulation models will be presented and discussed.
    Language: English
    Type: info:eu-repo/semantics/conferenceObject
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  • 8
    Publication Date: 2023-05-19
    Description: A recent study by Pedatella & Harvey (2022) investigated the influence of the stratospheric polar vortex on the mesosphere and the lower thermosphere (MLT) winds and tides using the Specified Dynamics Whole Atmosphere Community Climate Model with thermosphere-ionosphere eXtension (SD-WACCM-X) simulations. The model predicted that there would be a reduction in the migrating semidiurnal tide during strong polar vortex days, particularly at middle latitudes in the Northern Hemisphere. Here, we investigate this impact with unique observational datasets spanning 17 years of data collected in the MLT between 80-100 km by specular meteor radars at the middle (Germany, ~54°N) and high latitudes (Northern Norway, ~69°N). Correlation studies between Northern Annular Mode (NAM) at 10 hPa and estimated total amplitude of semidiurnal tidal anomalies are conducted at different altitudes. Preliminary results indicate that polar vortex strength slightly influences semidiurnal tidal anomalies but shows a clear altitude dependence on these influences. The analysis also suggests a stronger impact on weaker polar vortex days than on stronger days.
    Language: English
    Type: info:eu-repo/semantics/conferenceObject
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  • 9
    Publication Date: 2022-12-10
    Description: The 43rd UID conference, held in Genova, takes up the theme of ‘Dialogues’ as practice and debate on many fundamental topics in our social life, especially in these complex and not yet resolved times. The city of Genova offers the opportunity to ponder on the value of comparison and on the possibilities for the community, naturally focused on the aspects that concern us, as professors, researchers, disseminators of knowledge, or on all the possibile meanings of the discipline of representation and its dialogue with ‘others’, which we have broadly catalogued in three macro areas: History, Semiotics, Science / Technology. Therefore, “dialogue” as a profitable exchange based on a common language, without which it is impossible to comprehend and understand one another; and the graphic sign that connotes the conference is the precise transcription of this concept: the title ‘translated’ into signs, derived from the visual alphabet designed for the visual identity of the UID since 2017. There are many topics which refer to three macro sessions: - Witnessing (signs and history) - Communicating (signs and semiotics) - Experimenting (signs and sciences) Thanks to the different points of view, an exceptional resource of our disciplinary area, we want to try to outline the prevailing theoretical-operational synergies, the collaborative lines of an instrumental nature, the recent updates of the repertoires of images that attest and nourish the relations among representation, history, semiotics, sciences.
    Keywords: Discipline of representation, History, Semiotics, Science, Technology ; bic Book Industry Communication::G Reference, information & interdisciplinary subjects::GT Interdisciplinary studies::GTE Semiotics / semiology ; bic Book Industry Communication::H Humanities::HB History ; bic Book Industry Communication::P Mathematics & science::PD Science: general issues::PDR Impact of science & technology on society
    Language: Italian , English
    Format: image/jpeg
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  • 10
    Publication Date: 2024-04-14
    Description: Virtual reality
    Keywords: Computing & information technology ; thema EDItEUR::U Computing and Information Technology::UY Computer science::UYV Virtual reality
    Language: English
    Format: image/jpeg
    Format: image/jpeg
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