We conduct observational and modeling studies of thermospheric composition responses to weak geomagnetic activity (non-geomagnetic storms). We found that the thermospheric O and N 2 column density ratio (∑O/N 2 ) in part of the Northern Hemisphere measured by Global-scale Observations of the Limb and Disk (GOLD) exhibited large and long-lived depletions during weak geomagnetic activity in May and June 2019. The depletions reached 30% of quiet time values, extended equatorward to 10°N, and lasted more than 10 hours. Furthermore, numerical simulation results are similar to these observations and indicate that the ∑O/N 2 depletions were pushed westward by zonal winds. The ∑O/N 2 evolution during weak geomagnetic activity suggests that the formation mechanism of the ∑O/N 2 depletions is similar to that during a geomagnetic storm. The effects of weak geomagnetic activity are often ignored, but, in fact, are important for understanding thermosphere neutral composition variability and hence the state of the thermosphere-ionosphere system.

(top) The Kp and Dst index of three cases (DOY 145 to 148; DOY 153 to 156; DOY 162 to 165); (middle) latitude-longitude distribution of ∑O/N2 percentage difference between two quiet days in three cases; (bottom) percentage difference of ∑O/N2 between disturbed and quiet days in three cases. Corresponding local time is marked on longitude interval.

Publication Name: Geophysical Research Letter
First HAO Author's Name: Xuguang Cai
Other Authors: Alan G. Burns, Wenbin Wang, Liying Qian, Stanley C. Solomon Richard W. Eastes, Nicolas Pedatella, Robert E. Daniell, Will

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