On the Strength of Solar Forcing in the Earth's Thermosphere

Abstract We report the signature of solar forcing in the thermosphere using daytime temperature profiles from the Michelson Interferometer for Global High‐resolution Thermospheric Imaging (MIGHTI) instrument on NASA's Ionospheric Connection (ICON) Explorer mission. We compare temperatures from 90 to 133 km altitude with solar extreme ultraviolet flux and also with results from a Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIEGCM‐ICON) forced with MIGHTI wind and temperature observations at the bottom boundary near 97 km. For moderate solar activity in late 2021 to early 2022, MIGHTI temperature oscillations correlate with the 27‐day solar rotation period ( r = 0.84) at 133 km with an average amplitude of 38 K, more than twice the GCM amplitude for the same time period. At 110 km, average amplitudes are 8 K whereas the GCM shows insignificant correlation below 115 km (<0.3). These results reveal that solar forcing in the lower thermosphere is stronger than predicted.