Viscosity‐Driven Dynamics of the Midnight Temperature Maximum in the Low‐Latitude Thermosphere

Abstract This paper investigates the impact of viscosity on the dynamics of the Midnight Temperature Maximum (MTM) in the low‐latitude thermosphere. Our study utilizes simulations to examine how varying levels of viscosity influence neutral temperature patterns and horizontal wind behaviors, which, in turn, drive the MTM characterized by peak neutral temperatures around midnight. Findings indicate that lower viscosity levels lead to more pronounced temperature and wind pattern fluctuations, enhancing the magnitude of the MTM and advancing its peak occurrence to earlier than midnight. In contrast, higher viscosity levels dampen these fluctuations, resulting in more uniform temperature distributions and causing the MTM peak to be delayed to times after midnight. Further observations show that with both increasing latitude and altitude, the variability in the MTM's magnitude decreases with hemispheric asymmetries that grow with latitude and are modulated by magnetic field geometry, contrary to the expected behavior of thermospheric temperatures. This suggests a more uniform response to viscosity changes at different altitudes. Additionally, viscosity effects show latitude‐dependent characteristics; for instance, at higher viscosity levels, the zonal neutral wind profiles at low latitudes are significantly influenced by viscosity, impacting advection and convection, while meridional winds at higher latitudes show varied responses due to differential Joule heating effects, influencing energy dissipation and redistribution.