Investigation of interhemispheric asymmetry of the thermospheric composition observed by GOLD during the first strong geomagnetic storm in solar-cycle 25, 1: IMF By effects

Sigma O/N-2 depletion is more equatorward in the local morning than in the local afternoon in the northern hemisphere (NH), while more equatorward in the local afternoon than the local morning in the southern hemisphere (SH).

The Thermosphere Ionosphere Electrodynamics General Circulation Model simulations reproduced the observed Sigma O/N-2 asymmetry. The impacts of interplanetary magnetic field (IMF) east-west component (B-y) on the interhemispheric asymmetry of Sigma O/N-2 depletion was investigated. Comparisons of simulation results with and without real B-y show that the dominant positive IMF B-y results in the Joule heating maximum occurring in the local afternoon of NH and local morning in the SH during the storm initial phase, which generates the corresponding Sigma O/N-2 changes.