Investigation of different ΣO/N2 variations observed by GOLD during a minor geomagnetic storm from 2 to 4 August 2021

During a minor geomagnetic storm occurring from Aug 2 (day-of-year (DOY) 214) to Aug 4 (DOY 216), 2021, the National Aeronautics and Space Administration Global-scale Observations of the Limb and Disk (GOLD) mission observed different column density ratio of O to N-2 (Sigma O/N-2) variations in storm main and recovery phases. The percentage difference of Sigma O/N-2 between DOY 215 (disturbed day, main phase) and DOY 213 (quiet reference day) exhibits a depletion on the east side of the GOLD field-of-view (FOV).

However, that of Sigma O/N-2 between DOY 216 (recovery phase) and 213 shows depletions on the west side of GOLD FOV. The National Center for Atmospheric Research Thermosphere Ionosphere Electrodynamics General Circulation Model qualitatively reproduced the observations. Analysis of the model output illustrates that the Sigma O/N-2 patterns in the two days are both formed due to the classical thermospheric composition theory and formed on DOY 214 and 215, respectively.