Impact of Arctic and Antarctic Sudden Stratospheric Warmings on Thermospheric Composition

Abstract

Using the Global-scale Observations of the Limb and Disk (GOLD) and the Global Ultraviolet Imager (GUVI), we examine the impact of sudden stratospheric warmings (SSWs) on the changes of thermospheric composition during the 2018–2019 and 2020–2021 Arctic SSWs and the 2019 Antarctic SSW. Contributions of planetary waves, gravity waves, and migrating tides are assessed by performing numerical experiments with the NSF National Center for Atmospheric Research (NCAR) vertically extended version of the Whole Atmosphere Community Climate Model (WACCM-X). The variations in the column integrated O and N₂ density ratio ($\sum O/N_2$) are generally similar among WACCM-X, GOLD, and GUVI observations though some differences exist. Following the onset of the Arctic SSWs, $\sum O/N_2$ is reduced by $\sim$10% at low to mid latitudes. The variations during the 2019 Antarctic SSW are less pronounced, likely due to the event being a minor warming. WACCM-X simulations, with the Kp index and F10.7 cm solar flux kept at fixed low levels, confirm that the variability of $\sum O/N_2$ at low to mid latitudes is primarily induced by SSWs. The $\sum O/N_2$ changes are associated with the reversals of the mean meridional circulation (MMC) in the lower thermosphere, mainly driven by westward-traveling planetary waves. The results highlight that planetary wave activity during SSWs can significantly impact the mean state of the thermosphere.