Observations and simulations of the peak response time of thermospheric mass density to the 27-day solar EUV flux variation

In this study, the mass densities from Challenging Minisatellite Payload and Gravity Recovery and Climate Experiment satellites and the simulation results from the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) have been used to systematically explore the peak response time (or time delay hereafter) of thermospheric mass density to the 27-day solar extreme ultraviolet (EUV) flux variation. The TIEGCM can generally reproduce the observed time delay of thermospheric mass density to the 27-day solar EUV flux changes. The simulation results suggest that the delay of the peak of thermospheric mass density to that of the 27-day solar EUV flux variation is about 0.9 days. However, geomagnetic activity can significantly affect the derivation of the time delay of thermospheric mass density from the pure solar EUV flux impact. Additionally, the delay of thermospheric mass density to the 27-day solar EUV flux changes with altitude, latitude, and local time.