Direct Observational Evidence of Altered Mesosphere Lower Thermosphere
Mean Circulation from a Major Sudden Stratospheric Warming
Abstract
Sudden stratospheric warmings (SSWs) are large-scale phenomena
characterized by dramatic dynamic disruptions in the stratospheric
winter polar regions. Previous studies, especially those employing whole
atmosphere models, indicate that SSWs have strong impacts on the
circulation of the mesosphere lower thermosphere (MLT) and drive a
reversal in the mean meridional circulation (MMC) near 90-125 km
altitude. However, the robustness of these effects and the roles of
SSW-induced changes in global-scale wave activity to drive the reversal
have been difficult to observe simultaneously. This work employs
horizontal lower thermospheric (~93-106 km altitude)
winds near 10S-40N latitude from the Michelson Interferometer for Global
High-resolution Thermospheric Imaging (MIGHTI) instrument onboard the
Ionospheric Connection Explorer (ICON) to present observational evidence
of a prominent MLT MMC reversal associated with the January 2021 major
SSW event and to demonstrate connections to semidiurnal tidal activity
and possible associations with a ~3-day ultra-fast Kevin
wave (UFKW).