Evolution of Ionospheric Ion Upflow Flux During the April 2023 Geomagnetic Storm

Abstract We study the impact of the evolving magnetosphere‐ionosphere‐thermosphere system on upward ion fluxes during the 23–24 April 2023 geomagnetic storm. This storm has a “double‐dip” structure where two southward IMF periods cause two dips in the SYM‐H index. The auroral electrojet indices and field‐aligned currents reveal comparable ionospheric energy inputs during both dips. We use global total electron content maps to track mid‐to‐high‐latitude ionospheric density structures, which are known to have significant effects on upward ion fluxes. We find that each southward turning triggers a positive ionospheric storm phase. However, thermospheric O/N 2 depletions initiated during the 1st dip moderate the effects of magnetospheric driving on the ionosphere during the 2nd dip. Consequently, the density structures in the second positive phase are weaker and confined to lower latitudes than before. We use density and velocity measurements from DMSP satellites to identify regions with strong upward ion fluxes. We find that the storm‐enhanced density (SED) plume from the 1st dip drives significant upward fluxes when it crosses the open‐closed field line boundary. Comparable fluxes exist in the dawn sector due to large upward drifts driven by persistent energy inputs under strong negative conditions. We conclude that the evolution of storm‐time ion upflow flux has a local time dependency. The density‐regulated afternoon/evening sector fluxes are seeded by ionospheric high‐density structures and modulated by the thermospheric composition, while the velocity‐regulated dawn/morning sector fluxes are more consistent throughout the storm due to the steady magnetospheric driving under strong negative conditions.