9 results
Search Results
Now showing 1 - 9 of 9
- ItemLong-term studies of mesosphere and lower-thermosphere summer length definitions based on mean zonal wind features observed for more than one solar cycle at middle and high latitudes in the Northern Hemisphere(Katlenburg, Lindau : Copernicus, 2022) Jaen, Juliana; Renkwitz, Toralf; Chau, Jorge L.; He, Maosheng; Hoffmann, Peter; Yamazaki, Yosuke; Jacobi, Christoph; Tsutsumi, Masaki; Matthias, Vivien; Hall, ChrisSpecular meteor radars (SMRs) and partial reflection radars (PRRs) have been observing mesospheric winds for more than a solar cycle over Germany (g1/4g54g gN) and northern Norway (g1/4g69g gN). This work investigates the mesospheric mean zonal wind and the zonal mean geostrophic zonal wind from the Microwave Limb Sounder (MLS) over these two regions between 2004 and 2020. Our study focuses on the summer when strong planetary waves are absent and the stratospheric and tropospheric conditions are relatively stable. We establish two definitions of the summer length according to the zonal wind reversals: (1) the mesosphere and lower-thermosphere summer length (MLT-SL) using SMR and PRR winds and (2) the mesosphere summer length (M-SL) using the PRR and MLS. Under both definitions, the summer begins around April and ends around middle September. The largest year-to-year variability is found in the summer beginning in both definitions, particularly at high latitudes, possibly due to the influence of the polar vortex. At high latitudes, the year 2004 has a longer summer length compared to the mean value for MLT-SL as well as 2012 for both definitions. The M-SL exhibits an increasing trend over the years, while MLT-SL does not have a well-defined trend. We explore a possible influence of solar activity as well as large-scale atmospheric influences (e.g., quasi-biennial oscillation (QBO), El NiƱo-Southern Oscillation (ENSO), major sudden stratospheric warming events). We complement our work with an extended time series of 31 years at middle latitudes using only PRR winds. In this case, the summer length shows a breakpoint, suggesting a non-uniform trend, and periods similar to those known for ENSO and QBO.
- ItemMesospheric gravity wave activity estimated via airglow imagery, multistatic meteor radar, and SABER data taken during the SIMONeā2018 campaign(Katlenburg-Lindau : European Geosciences Union, 2021) Vargas, Fabio; Chau, Jorge L.; Charuvil Asokan, Harikrishnan; Gerding, MichaelWe describe in this study the analysis of small and large horizontal-scale gravity waves from datasets composed of images from multiple mesospheric airglow emissions as well as multistatic specular meteor radar (MSMR) winds collected in early November 2018, during the SIMONe-2018 (Spread-spectrum Interferometric Multi-static meteor radar Observing Network) campaign. These ground-based measurements are supported by temperature and neutral density profiles from TIMED/SABER (Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry) satellite in orbits near KĆ¼hlungsborn, northern Germany (54.1 N, 11.8 E). The scientific goals here include the characterization of gravity waves and their interaction with the mean flow in the mesosphere and lower thermosphere and their relationship to dynamical conditions in the lower and upper atmosphere. We have obtained intrinsic parameters of small- and large-scale gravity waves and characterized their impact in the mesosphere via momentum flux (FM) and momentum flux divergence (FD) estimations. We have verified that a small percentage of the detected wave events is responsible for most of FM measured during the campaign from oscillations seen in the airglow brightness and MSMR winds taken over 45 h during four nights of clear-sky observations. From the analysis of small-scale gravity waves (Ī»h < 725 km) seen in airglow images, we have found FM ranging from 0.04-24.74 m2 s-2 (1.62 Ā± 2.70 m2 s-2 on average). However, small-scale waves with FM > 3 m2 s-2 (11 % of the events) transport 50 % of the total measured FM. Likewise, wave events of FM > 10 m2 s-2 (2 % of the events) transport 20 % of the total. The examination of large-scale waves (Ī»h > 725 km) seen simultaneously in airglow keograms and MSMR winds revealed amplitudes > 35 %, which translates into FM Combining double low line 21.2-29.6 m2 s-2. In terms of gravity-wave-mean-flow interactions, these large FM waves could cause decelerations of FD Combining double low line 22-41 m s-1 d-1 (small-scale waves) and FD Combining double low line 38-43 m s-1 d-1 (large-scale waves) if breaking or dissipating within short distances in the mesosphere and lower thermosphere region. Ā© 2021 Fabio Vargas et al.
- ItemHorizontal Wavenumber Spectra of Vertical Vorticity and Horizontal Divergence of Mesoscale Dynamics in the Mesosphere and Lower Thermosphere Using Multistatic Specular Meteor Radar Observations(Malden, Mass. : American Geophysical Union, 2022) Poblet, Facundo L.; Chau, Jorge L.; Conte, J. Federico; Avsarkisov, Victor; Vierinen, Juha; Charuvil Asokan, HarikrishnanSpecular 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 ā¼50ā400 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.
- ItemQuasiā2āDay Wave in LowāLatitude Atmospheric Winds as Viewed From the Ground and Space During JanuaryāMarch, 2020(Hoboken, NJ : Wiley, 2021) He, Maosheng; Chau, Jorge L.; Forbes, Jeffrey M.; Zhang, Xiaoli; Englert, Christoph R.; Harding, Brian J.; Immel, Thomas J.; Lima, Lourivaldo M.; Bhaskar Rao, S. Vijaya; Ratnam, M. Venkat; Li, Guozhu; Harlander, John M.; Marr, Kenneth D.; Makela, Jonathan J.Horizontal winds from four low-latitude (Ā±15Ā°) specular meteor radars (SMRs) and the Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) instrument on the ICON satellite, are combined to investigate quasi-2-day waves (Q2DWs) in early 2020. SMRs cover 80ā100 km altitude whereas MIGHTI covers 95ā300 km. Q2DWs are the largest dynamical feature of the summertime middle atmosphere. At the overlapping altitudes, comparisons between the derived Q2DWs exhibit excellent agreement. The SMR sensor array analyses show that the dominant zonal wavenumbers are s = +2 and + 3, and help resolve ambiguities in MIGHTI results. We present the first Q2DW depiction for s = +2 and s = +3 between 95 and 200 km, and show that their amplitudes are almost invariant between 80 and 100 km. Above 106 km, Q2DW amplitudes and phases present structures that might result from the superposition of Q2DWs and their aliased secondary waves.
- ItemThe future of auroral E-region plasma turbulence research(Lausanne : Frontiers Media, 2022) Huyghebaert, Devin; Billett, Daniel; Chartier, Alex; Chau, Jorge L.; Hussey, Glenn C.; Hysell, David L.; Ivarsen, Magnus F.; Mesquita, Rafael L. A.; Rojas, Enrique; Vierinen, Juha; Young, MatthewThe heating caused by ionospheric E-region plasma turbulence has documented global implications for the energy transfer from space into the terrestrial atmosphere. Traveling atmospheric disturbances, neutral wind motion, energy deposition rates, and ionospheric conductance have all been shown to be potentially affected by turbulent plasma heating. Therefore it is proposed to enhance and expand existing ionospheric radar capabilities and fund research into E-region plasma turbulence so that it is possible to more accurately quantify the solar-terrestrial energy budget and study phenomena related to E-region plasma turbulence. The proposed research funding includes the development of models to accurately predict and model the E-region plasma turbulence using particle-in-cell analysis, fluid-based analysis, and hybrid combinations of the two. This review provides an expanded and more detailed description of the past, present, and future of auroral E-region plasma turbulence research compared to the summary report submitted to the National Academy of Sciences Decadal Survey for Solar and Space Physics (Heliophysics) 2024ā2033 (Huyghebaert et al., 2022a).
- ItemImproving ionospheric predictability requires accurate simulation of the mesospheric polar vortex(Lausanne : Frontiers Media, 2022) Harvey, V. Lynn; Randall, Cora E.; Bailey, Scott M.; Becker, Erich; Chau, Jorge L.; Cullens, Chihoko Y.; Goncharenko, Larisa P.; Gordley, Larry L.; Hindley, Neil P.; Lieberman, Ruth S.; Liu, Han-Li; Megner, Linda; Palo, Scott E.; Pedatella, Nicholas M.; Siskind, David E.; Sassi, Fabrizio; Smith, Anne K.; Stober, Gunter; Stolle, Claudia; Yue, JiaThe mesospheric polar vortex (MPV) plays a critical role in coupling the atmosphere-ionosphere system, so its accurate simulation is imperative for robust predictions of the thermosphere and ionosphere. While the stratospheric polar vortex is widely understood and characterized, the mesospheric polar vortex is much less well-known and observed, a short-coming that must be addressed to improve predictability of the ionosphere. The winter MPV facilitates top-down coupling via the communication of high energy particle precipitation effects from the thermosphere down to the stratosphere, though the details of this mechanism are poorly understood. Coupling from the bottom-up involves gravity waves (GWs), planetary waves (PWs), and tidal interactions that are distinctly different and important during weak vs. strong vortex states, and yet remain poorly understood as well. Moreover, generation and modulation of GWs by the large wind shears at the vortex edge contribute to the generation of traveling atmospheric disturbances and traveling ionospheric disturbances. Unfortunately, representation of the MPV is generally not accurate in state-of-the-art general circulation models, even when compared to the limited observational data available. Models substantially underestimate eastward momentum at the top of the MPV, which limits the ability to predict upward effects in the thermosphere. The zonal wind bias responsible for this missing momentum in models has been attributed to deficiencies in the treatment of GWs and to an inaccurate representation of the high-latitude dynamics. In the coming decade, simulations of the MPV must be improved.
- ItemHigh-Order Solar Migrating Tides Quench at SSW Onsets(Hoboken, NJ : Wiley, 2020) He, Maosheng; Forbes, Jeffrey M.; Chau, Jorge L.; Li, Guozhu; Wan, Weixing; Korotyshkin, Dmitry V.Sudden stratospheric warming events (SSWs) are the most spectacular atmospheric vertical coupling processes, well-known for being associated with diverse wave activities in the upper atmosphere and ionosphere. The first four solar tidal harmonics have been reported as being engaged. Here, combining mesospheric winds detected by three midlatitude radars, we demonstrate at least the first six harmonics that occurred during SSW 2018. Wave number diagnosis demonstrates that all six harmonics are dominated by migrating components. Wavelet analyses reveal that the fourth, fifth, and sixth harmonics quench after the SSW onset. The six harmonics and the quenching appear also in a statistical analysis based on near-12-year observations from one of the radars. We attribute the quenching to reversal of the background eastward wind. Ā©2020. The Authors.
- ItemQuasiā10āDay Wave and Semidiurnal Tide Nonlinear Interactions During the Southern Hemispheric SSW 2019 Observed in the Northern Hemispheric Mesosphere(Hoboken, NJ : Wiley, 2020) He, Maosheng; Chau, Jorge L.; Forbes, Jeffrey M.; Thorsen, Denise; Li, Guozhu; Siddiqui, Tarique Adnan; Yamazaki, Yosuke; Hocking, Wayne K.Mesospheric winds from three longitudinal sectors at 65Ā°N and 54Ā°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. Ā© 2020. The Authors.
- ItemDetermination of the Azimuthal Extent of Coherent EāRegion Scatter Using the ICEBEAR Linear Receiver Array(Hoboken, NJ : Wiley, 2021) Huyghebaert, Devin; McWilliams, Kathryn; Hussey, Glenn; Galeschuk, Draven; Chau, Jorge L.; Vierinen, JuhaThe Ionospheric Continuous-wave E-region Bistatic Experimental Auroral Radar (ICEBEAR) is a VHF coherent scatter radar that operates with a field-of-view centered on 58Ā°N, 106Ā°W and measures characteristics of ionospheric E-region plasma density irregularities. The initial operations of ICEBEAR utilized a wavelength-spaced linear receiving array to determine the angle of arrival of the ionospheric scatter at the receiver site. Initially only the shortest baselines were used to determine the angle of arrival of the scatter. This publication uses this linear antenna array configuration and expands on the initial angle of arrival determination by including all the cross-spectra available from the antenna array to determine both the azimuthal angle of arrival and the azimuthal extent of the incoming ionospheric scatter. This is accomplished by fitting Gaussian distributions to the complex coherence of the signal between different antennas and deriving the azimuthal angle and extent based on the best fit. Fourteen hours of data during an active ionospheric period (March 10, 2018, 0ā14 UT) were analyzed to investigate the Gaussian fitting procedure and determine its feasibility for implementation with ICEBEAR. A comparison between mapped scatter, both neglecting azimuthal extent and including azimuthal extent is presented. It demonstrates that the azimuthal extent of the ionospheric E-region scatter is very important for accurately portraying and analyzing the ICEBEAR measurements.