ST3.6

Planetary wave (PW) associated dynamical variability in the equatorial and extratropical middle atmosphere during the September 2019 Southern hemisphere minor sudden stratospheric warming (SSW) is investigated utilizing meteor radar wind observations from São João do Cariri (7.4°S, 36.5°W) and Cachoeira Paulista (22.7°S, 45°W) and reanalysis data. Signature of the mesospheric warming in conjunction with the stratospheric cooling is found at low latitudes. The strong westerly wind at low latitudes decelerates notably near 65 km at the onset of the warming episode, although no wind reversal is observed. The wind spectra reveal a prevalent quasi-16-day wave (Q16DW) prior to the SSW and existence of a quasi-6-day wave (Q6DW) after the warming event. Possible existence of barotropic/baroclinic instability in the low and mid latitude middle atmosphere may be responsible for exciting the Q6DW. The traveling PW is primarily found to travel westward corresponding to zonal wavenumber 1 and 2. Furthermore, significant latitudinal mixing of airmass between the tropics and high latitudes is evident in the potential vorticity map. The Eliassen-Palm flux diagnosis shows the propagation of the Q6DW and Q16DW from mid to low latitudes during the warming event.

How to cite: Mitra, G., Guharay, A., Batista, P., and Buriti, R.: Response of the traveling planetary waves at low latitude middle atmosphere during September 2019 minor sudden stratospheric warming, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11510, https://doi.org/10.5194/egusphere-egu22-11510, 2022.

     Gravity waves (GW) couple various atmospheric layers and influence dynamics of the region in which they dissipate their energy. Attenuation of GW is in this contribution calculated from the ratio of GW kinetic energies observed at different heights by multi-frequency and multi-point continuous Doppler sounding that allows three-dimensional (3D) analysis of GW propagation in the ionosphere. It is shown that the attenuation of GWs increases with height, which is consistent with the hypothesis that mainly viscous damping and losses due to thermal conductivity are responsible for the wave attenuation in the thermosphere/ionosphere. The kinematic viscosity of the highly rarefied air at the height of observation is estimated from the observed attenuation with altitude and complex dispersion relation for GWs that includes viscosity and thermal conductivity, which is linked with the viscosity via Prandtl number. The intrinsic (wind rest frame) characteristics of GW that enter the dispersion relation are obtained after subtracting the neutral wind velocities from the observed phase velocities using HWM-14 wind model. A more detailed modelling of GW attenuation will be done in the future. 

How to cite: Chum, J., Fagre, M., Podolska, K., and Rusz, J.: Attenuation of gravity waves and kinetic viscosity in the ionosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1317, https://doi.org/10.5194/egusphere-egu22-1317, 2022.

Sporadic E or Es is a transient phenomenon where thin layers of enhanced electron density appear in the ionospheric E region (90-120 km altitude). Es can influence radio propagation, and its global characteristics have been of great interest to radio communications and navigations. The presence of neutral wind shear caused by atmospheric tides will lead ions to converge at E-region heights and form Es layers.The neutral wind shear caused by atmospheric tides can lead ions to converge vertically at E-region heights and form the Es layers. This research aims to determine the role of atmospheric solar and lunar tides in Es occurrence. For this purpose, radio occultation data of FORMASAT-3/COSMIC have been used, which provides complete global coverage of Es events. Moreover, GAIA model simulations have been employed to evaluate the vertical ion convergence induced by solar tides. The results show both migrating and non-migrating solar tidal signatures and the semidiurnal migrating lunar tidal signature in Es occurrence. The seasonal variations of the diurnal and semidiurnal solar migrating components of Es are in good agreement with those in the zonal wind shear. Furthermore, some non-migrating components of solar tides also have a significant effect on the Es occurrence rate.

How to cite: Sobhkhiz-Miandehi, S., Yamazaki, Y., Arras, C., Miyoshi, Y., and Shinagawa, H.: Comparison of the Tidal Signatures in Sporadic E and Vertical Ion Convergence Rate, Using FORMASAT-3/COSMIC Radio Occultation Observations and GAIA Model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1942, https://doi.org/10.5194/egusphere-egu22-1942, 2022.

In this study, the variability of migrating solar diurnal (DW1) tide in the mesosphere-lower thermosphere (MLT) region during Northern and Southern Hemisphere (NH & SH) Sudden Stratospheric Warmings (SSWs) is investigated using Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperature  observations and reanalysis-driven Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM-X) simulations. The periods examined include four major NH SSWs that occurred during January in 2006, 2009, 2010 and 2013 and two SH SSWs that were recorded in September in 2002 and 2019. Our analysis shows that the observed DW1 tide displays a marked decline in the equatorial region after the onset of NH and SH SSWs. As WACCM-X simulations qualitatively reproduce this feature of DW1 tidal variability common to both NH and SH SSWs, they have been used to examine the possible mechanism that could explain these observations in DW1 tide. It is known that changes in the latitudinal shear of zonal winds at low-latitudes strongly affect the seasonal variation of DW1 tide in the MLT. We explore this mechanism to show that SSW-associated changes in the latitudinal shear in the MLT could be used to explain the observed variability of DW1 tide during NH and SH SSWs.

How to cite: Siddiqui, T. A., Stolle, C., and Yamazaki, Y.: Migrating solar diurnal tidal variability during Northern and Southern Hemisphere Sudden Stratospheric Warmings, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11327, https://doi.org/10.5194/egusphere-egu22-11327, 2022.

Sporadic E (Es) is a thin layer of metallic ion plasma that forms in the E region of the Earth’s ionosphere, mostly between 90 and 125 km. It can affect the radio frequencies in the HF range of up to 30 MHz. In the mid-latitudes, the wind shear mechanism causes the formation of the Es layers. In general, solar forcing primarily controls changes in the E layer. On the other hand, the formation of the mid-latitude Es layer is driven by the wind shear associated with lower atmosphere originated wave activities. Since the formation of the Es layer is caused by the lower atmospheric forcing, it can be used as a tracer to estimate the lower atmospheric impact on the upper mesosphere and lower thermosphere (UMLT). Therefore, the study of the long-term changes and trends (if any) in the E and Es layers will throw some light on the effect of the lower atmosphere and solar forcing on the UMLT region.

In the present study, we investigate the long-term variation and trends in the E region, using sixty-three years of continuous ionosonde observations over Juliusruh (54.6° N 13.4° E), Europe. Before the trend analysis, predominant long-term variations are estimated using the Lomb-Scargle periodogram analysis. We found that the annual and solar cycle oscillations are strongly present in both foE and foEs. In addition, a weak semi-annual oscillation is also noted in the foE.  Furthermore, the model time series data of foE and foEs is created using the period and amplitude of the predominant oscillations. Then, the residual value of foE and foEs is calculated by subtracting the model values from the observation. By using the least square fit analysis, the trend is estimated. Interestingly, weak negative trends in the foE and foEs are found. The plausible causative mechanism for the observed trends will be detailed in the presentation.

How to cite: Sivakandan, M., Mielich, J., Renkwitz, T., and Chau, J. L.: Long-term variations and trends in the E and sporadic E layer over Juliusruh (54° N), Europe, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5895, https://doi.org/10.5194/egusphere-egu22-5895, 2022.

This study investigates the role of hotspots in stratospheric gravity waves (GWs) in the generation of traveling ionospheric disturbances (TIDs) at middle latitudes. We utilize observations of GWs at 35 km altitude by the Atmospheric InfraRed Sounder (AIRS) on NASA’s Aqua satellite to characterize stratospheric gravity wave activity. The evolution of GWs with altitudes extending from the stratosphere to mesosphere-lower-thermosphere (MLT) region is examined using temperature observations from the Sounding of the Atmosphere using Broadband Emission Radiometry instrument. Ground-based total electron content observations from GNSS receivers are used to characterize TID activity in the ionosphere. Simulations by the High Altitude Mechanistic general Circulation Model (HIAMCM) that is nudged to the Modern-Era Retrospective analysis for Research and Applications version 2 (MERRA-2) reanalysis in the troposphere and stratosphere are used to study multi-step vertical coupling between the stratosphere and the thermosphere.  We investigate two case studies, the Arctic winter of 2016/2017 when a sudden stratospheric warming developed in January-February 2017, and the winter of 2019/2020 that was characterized by mostly strong polar vortex conditions. The hotspot in stratospheric GWs peaks at 55-75N at the edge of polar vortex and in a limited range of longitudes.  Our results indicate that GW activity evolves with altitude and expands to 35-40N in the MLT region. Amplifications of TIDs during times of high stratospheric GW activity are seen from ~25-30N to 60N. HIAMCM simulations indicate a very good agreement with observations in the timing of GW activity and latitudinal coverage. We conclude that TIDs are generally amplified during high stratospheric GW activity and weakened during the periods of low stratospheric GW activity (during and after SSW).

How to cite: Goncharenko, L., Harvey, V. L., Cullens, C., Becker, E., Zhang, S.-R., and Coster, A.: Influence of stratospheric gravity waves on TID activity at middle latitudes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6823, https://doi.org/10.5194/egusphere-egu22-6823, 2022.

The polar vortices play a central role in vertically coupling the Sun-Earth system by facilitating the descent of reactive odd nitrogen (NO_x = NO + NO₂) produced in the atmosphere by energetic particle precipitation (EPP-NO_x). Downward transport of EPP-NO_x from the mesosphere-lower thermosphere (MLT) to the stratosphere inside the winter polar vortex is particularly impactful in the wake of prolonged sudden stratospheric warming (SSW) events. This work is motivated by the fact that state-of-the-art global climate models severely underestimate EPP-NO_x abundances in the polar MLT. It is not clear whether this deficiency is due to a missing NO_x source or to inadequate transport processes. As a step toward understanding the transport pathways by which MLT air enters the top of the polar vortex, we explore the extent to which planetary waves impact the geographic distribution of NO near the polar winter mesopause in the Whole Atmosphere Community Climate Model with thermosphere-ionosphere eXtension combined with data assimilation using the Data Assimilation Research Testbed (WACCMX+DART). We present planetary wave-driven NO patterns near the polar winter mesopause during 16 case studies from the Arctic winters of 2005/2006 through 2018/2019. During all cases the model is in reasonable agreement with Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) derived zonal winds and Solar Occultation For Ice Experiment (SOFIE) and Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS) NO measurements. Superposed Epoch Analysis is employed to diagnose typical mesopause planetary wave behavior and vertical transport characteristics during 10 minor and 6 major SSW events. Results show that descent of NO into the top of the polar vortex is enhanced by about a factor of 4 in traveling planetary wave troughs vs. in ridges and that this planetary wave-driven enhanced NO descent occurs during both minor and major SSW events. These results present a new conceptual model of zonally varying, vs. zonally uniform, polar descent in the MLT.

How to cite: Harvey, V. L., Pedatella, N., Datta-Barua, S., Randall, C., Siskind, D., Greer, K., and Goncharenko, L.: Planetary wave-driven enhanced NO descent into the top of the Arctic polar vortex during major and minor sudden stratospheric warmings, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1136, https://doi.org/10.5194/egusphere-egu22-1136, 2022.

A newly established multi-static meteor radar network, CONDOR (31.2ºS,70.0ºW), provides the capability to resolve wind and temperature oscillations over a broad range of periods, calculate E-P flux of planetary waves and investigate the short-term variability in the 80-100 km MLT region. In this study we present results of an enhanced westward wavenumber 1 Q6DW activity and its modulation with the amplified diurnal tides and gravity waves (GW) meridional wind variance during a rare minor SH SSW in 2019, using two SH midlatitude meteor radar observations and a recently developed 3DVAR algorithm. This algorithm creates a tomographic reconstruction of the 3D wind field based on optimal estimation technique and Bayesian statistics and is particularly suitable for investigating GW dynamics on regional scales. Furthermore, we present the first results of meteor radar observed Q6DW E-P flux and its comparison with SD-WACCM-X simulated Q6DW E-P flux. The encouraging agreement demonstrated that this SSW-related Q6DW activity had a significant impact on the dynamically coupled MLT region at SH midlatitude.

How to cite: Qiao, Z., Liu, A. Z., Pedatella, N., Stober, G., Reid, I., Fuentes, J., and Adami, C.: Enhanced Quasi-6-Day Wave during the 2019 Southern Hemisphere SSW and its modulation of diurnal tides and gravity waves, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10996, https://doi.org/10.5194/egusphere-egu22-10996, 2022.