Ionosphere-Thermosphere Response to the Interaction Between a Geomagnetic Storm and Sudden Stratospheric Warming

This study examines how preconditioning from a Sudden Stratospheric Warming (SSW) alters the ionosphere-thermosphere (IT) response to a geomagnetic storm using the Specified Dynamics version of the Whole Atmosphere Community Climate Model (SD-WACCM-X). Two simulations were performed to study the 2022–2023 Northern Hemisphere winter, when a strong geomagnetic storm (Kp ∼ 6) coincided with the occurrence of an SSW. One simulation included the SSW by nudging the lower atmosphere to MERRA-2 reanalysis data for January–March 2023, while the other used January–March 2022 MERRA-2 data to represent no SSW. Both simulations used the same solar and geomagnetic conditions for January–March 2023. Comparison of the two reveals that the storm responses in thermosphere composition and electron density can differ by up to 20%–50% due to the SSW preconditioning. The simulation including the SSW exhibits faster storm-time recovery, consistent with earlier studies, indicating that lower-atmosphere forcing influences storm-time IT dynamics. This study further examines how SSW influences storm-time processes. Under SSW conditions at mid-to-high latitudes, the thermosphere is cooler, and electron density is reduced relative to the no-SSW case, lowering conductivity, weakening storm-time Joule heating, and reinforcing thermospheric cooling. Thus, both SSW-induced background modifications and storm-background interactions shape the storm-time temperature and meridional circulation and thus thermosphere composition that is, ΣO/N₂, which then influences electron density through ion-neutral chemistry. At lower latitudes, the SSW modifies E × B ion transport and the ion loss through recombination, both of which are key drivers of electron density changes. Consideration of lower-atmosphere variability is therefore essential for understanding the storm-time IT response.