Storm-time Variation of 𝚺O/N₂ Transition Latitude Observed by GOLD and ICON

This research examines the upper atmospheric responses to geomagnetic storms through analysis of the column-integrated O/N2 ratio (ΣO/N2). Data products from NASA’s Ionospheric Connection Explorer (ICON) and Global-scale Observations of the Limb and Disk (GOLD) missions are analyzed to characterize storm-time changes in thermospheric composition. During geomagnetically disturbed periods, the thermosphere exhibits a pronounced latitudinal structure, with reduced ΣO/N2 in high-latitude region and enhanced ΣO/N2 equatorward. These dynamic changes are observed in the GOLD disk views as a distinct latitudinal banded pattern, a “Pepsi-like” structure.
To quantify the response of the thermosphere to the geomagnetic storms, we introduce the concept of the “transition latitude”, where the storm-time change in ΣO/N2 relative to background condition (∆ΣO/N2) transitions from negative to positive values toward the equator. . Analysis of geomagnetic storm events (Kp >= 5) during 2018~2025 reveals that the location of the transition latitude generally shifts equatorward with increasing levels of geomagnetic storm activity, while seasonal effects also contribute to the hemispheric asymmetry in the transition latitude. This study demonstrates that the transition latitude provides a quantitative metric for characterizing global thermospheric composition responses to geomagnetic storm events.