Terrestrial Impacts on Large-Scale Structures in the Thermosphere from Swarm-C and Connections to the Topside Ionosphere from DMSP

The terrestrial and lower atmospheric processes generally govern the variability in the ionosphere-thermosphere (IT) system through momentum transfer, ion-neutral mixing, and longitudinal-vertical coupling during quiet days. Understanding the variability and impact of large-scale waves on neutral and plasma structures in the IT system is crucial for improving operational forecasting, satellite drag, and ionospheric irregularities. In this study, the longitudinal patterns of large-scale tidal waves in the low-latitude ionosphere/thermosphere are investigated using the electron and neutral density data from Defense Meteorological Satellite Program - F18 (DMSP-F18) and Swarm-C (ESA Earth Explorer mission) satellites respectively. A least-square data fitting technique is employed to examine wave mode structures of neutrals in the thermosphere and electrons in the topside ionosphere for the geomagnetically quiet years of 2020 and 2021. The wavenumber (WN) patterns are extracted and presented by fitting the longitudinal distribution of the electron and neutral density profiles in the low-latitude (±10°) regions. The analysis shows that the wavenumber structures during the daytime and the nighttime are observed with different strengths. The study of the wave mode structures of electrons and neutrals at the two different altitudinal ranges can address many questions regarding the dynamical coupling of terrestrial/tropospheric variability with low-latitude IT neutral and electron density variability. Furthermore, the derived large-scale structure patterns from satellite-borne instruments are compared with the results from the state-of-the-art Specified-Dynamics (SD) Whole Atmosphere Community Climate Model with thermosphere and ionosphere eXtension (WACCM-X) simulations under similar conditions. Based on measured and simulated evidence, we discuss the potential sources, possible propagation, interactions, and perturbation mechanisms of the WN mode structures controlled by various forms of terrestrial sources.