Variation of the Column O/N₂ Transition Latitude During Geomagnetic Storms

This research aims to examines the atmospheric and ionospheric responses to geomagnetic storms through analysis of the O-to-N₂ ratio (ON2). Data products from NASA’s Ionospheric Connection Explorer (ICON) and Global-scale Observations of the Limb and Disk (GOLD) missions are analyzed to capture these variations. During geomagnetic storm events, the atmosphere exhibits latitudinally dependent behavior, characterized by expansion in high-latitude regions and compression near the equator. These dynamic changes are reflected in variations of the column ON2 often forming a distinct “Pepsi-like” structure in the GOLD disk views. The transition latitude, defined as the latitude where atmospheric behavior shifts from compression to expansion, is introduced to quantify the response of the thermosphere to geomagnetic storms. This study explores the relationship between storm strength, as indicated by geomagnetic indices (mean standardized K-index, auroral electrojet index, and disturbance storm time), and the emergence of the Pepsi-like ON2 pattern as well as the transition latitude. Using storm cases (AE > 400 nT) during ICON mission lifetime (December 2019 to November 2022), preliminary results show that 1) not all storms create the “Pepsi-like” structure; 2) seasonal factors may play a role in the variation of the transition latitude in both hemisphere. Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM) will be included for a data-model comparison and mechanism investigation.