Atmospheric Tides in the Thermosphere: Forcing From Above Versus Forcing From Below

Abstract This study investigates the relative importance of lower atmospheric versus in situ forcing in driving migrating and nonmigrating diurnal and semidiurnal tides in the thermosphere, as well as the impact of solar and geomagnetic activity on these tides. Our focus is the “thermospheric gap” region 110–250 km, where few observations are available but the tidal spectrum is known to change dramatically. We employ the Hough Mode Extension (HME) fitting approach to the Specified Dynamics Whole Atmosphere Community Climate Model with thermosphere‐ionosphere eXtension (SD‐WACCM‐X) to separate upward‐propagating tides originating from tropospheric and stratospheric sources from those generated in situ within the thermosphere and calculate their ratio to quantify their relative importance. To assess the extent to which the solar and geomagnetic activity impact these thermospheric tides, we compare SD‐WACCM‐X simulations with control simulations in which geomagnetic (Kp) and solar (F10.7) activity are held at lower fixed values. Focusing on the year 2014, a period characterized by elevated solar and geomagnetic variability, we analyze how these external drivers modify tidal amplitudes as a function of latitude and season. The model simulations are validated by comparison with independent neutral density tide observations from the CHAllenging Minisatellite Payload data at approximately 390 km altitude from 2002 to 2004 (F10.7 = 140 sfu). The results highlight the critical role of both thermospheric and lower atmospheric forcings in shaping tidal dynamics, which has implications for forthcoming satellite missions targeting the space weather of the ionosphere‐thermosphere system and improving space operations in the very low Earth orbit.