Different peak response time of daytime thermospheric neutral species to the 27-day solar EUV flux variations

In this study, we used the Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM) to explore the physical mechanisms responsible for the different peak response times of the daytime thermospheric neutral species.

It was found that the peak response time of O or N(2)mass density corresponds to the time of equilibrium between the contributions from the barometric effect and the change in its abundance. The peak response time of O is shorter than that of thermospheric temperature Tn, due to a dynamic change in the circulation that acts to cancel out the contribution from the barometric process prior to the peak of Tn. On the contrary, the change of N(2)abundance contributes further to a decrease of N(2)mass density on a constant pressure surface when the thermosphere is expanding.