Quasi-10-day wave activity in the southern high-latitude MLT region and its relation to the large-scale instability and gravity wave drag

• Main Authors: Lee, Wonseok, Song, In-Sun, Song, Byeong-Gwon, Kim, Yong Ha
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2023
• Subjects: article; Verlagsveröffentlichung; Antarc*; Antarctica
• Online Access: https://doi.org/10.5194/egusphere-2023-2381; https://noa.gwlb.de/receive/cop_mods_00069504; https://noa.gwlb.de/servlets/MCRFileNodeServlet/cop_derivate_00067888/egusphere-2023-2381.pdf; https://egusphere.copernicus.org/preprints/2023/egusphere-2023-2381/egusphere-2023-2381.pdf

Seasonal variation of westward-propagating quasi-10-day wave (Q10DW) in the mesosphere and lower thermosphere of the Southern Hemisphere (SH) high-latitude regions is investigated using meteor radar (MR) observations for the period of 2012–2016 and Specified Dynamics (SD) version of the Whole Atmosphere Community Climate Model (WACCM). The phase difference of meridional winds measured by two MRs located in Antarctica gives observational estimates of the amplitude and phase of Q10DW with zonal wavenumber 1 (W1). The amplitude of the observed Q10DW-W1 is large around equinoxes. In order to elucidate the variations of the observed Q10DW-W1 and its possible amplification mechanism, we carry out two SD-WACCM experiments nudged towards the MERRA-2 reanalysis from the surface up to ~60 km (EXP60) and ~75 km (EXP75). Results of the EXP75 indicate that the observed Q10DW-W1 can be amplified around the barotropic/baroclinic instability regions in the middle mesosphere around 60° S–70° S. In the EXP60, it is also found that Q10DW-W1 is amplified around the instability regions, but the amplitude is too large compared with MR observations. The large-scale instability in the EXP60 in the SH summer mesosphere is stronger than that in the EXP75 and Microwave Limb Sounder observation. The larger instability in the EXP60 is related to the large meridional and vertical variations of polar mesospheric zonal winds in associated with gravity wave parameterization (GWP). Given uncertainties inherent in GWP, these results can suggest that it is possible for models to spuriously generate traveling planetary waves such as Q10DW, especially in summer, due to the excessively strong large-scale instability in the SH high-latitude mesosphere.