Substorm evolution as viewed from a data assimilation technique, Lompe.

Substorms are transient, explosive events during which energy accumulated in the magnetosphere is rapidly released and dissipated in the high-latitude ionosphere. These events typically last 1–2 hours and may occur several times per day. Despite extensive observational and theoretical efforts, the physical processes governing substorm onset in the magnetosphere and the coupled ionospheric response remain incompletely understood. In particular, the spatiotemporal evolution of electrodynamic parameters during substorms and their dependence on solar wind driving require further investigation.

In this study, we integrate satellite and ground-based observations with the data assimilation technique, Local Mapping of Polar Ionospheric Electrodynamics (Lompe), to examine the global evolution of ionospheric electrodynamics during substorm events. Using Lompe, we reconstruct maps of ionospheric electric potential, ionosphere convection patterns, and field-aligned current systems, and analyze their temporal development throughout substorm phases. These parameters are analyzed in relation to the orientation of the interplanetary magnetic field (IMF). In addition, magnetospheric dynamics during substorms is inferred from estimates of the reconnection electric field, derived by calculating magnetic flux transfer across the open–closed field line boundary.

Our results provide a comprehensive global characterization of the polar ionospheric response to substorms and offer additional insights into the coupling between magnetospheric reconnection processes and ionospheric electrodynamics.