Polar Sporadic E Layers and Auroral Substorm Activity: Statistical Relationships and Possible Modulation Processes

Abstract

This study investigates the relationship between polar sporadic E (Es) layers and auroral substorm activity using long‐term satellite observations. Polar Es layer occurrence exhibits a pronounced annular enhancement that closely resembles the climatological distribution of auroral substorm onset locations, with the Es enhancement displaced poleward by approximately 10°; both distributions also show a pronounced dusk‐to‐midnight preference. Despite this climatological correspondence, superposed epoch analysis shows that Es layer occurrence decreases following individual substorm onsets. Collocated DMSP observations further reveal no positive dependence of Es layer occurrence on energetic electron or ion precipitation, indicating that precipitation‐induced ionization alone is insufficient to promote polar Es layer formation. In contrast, Es layer occurrence increases with increasing auroral electrojet (AE) and expands equatorward under enhanced AE activity. The altitude–MLT distributions exhibit coherent downward phase progression consistent with semidiurnal tidal modulation; under enhanced AE conditions, the nighttime tidal signature persists, while more irregular structures emerge. These contrasting responses demonstrate that the climatological association between polar Es layers and substorm activity does not represent direct triggering by individual substorms or energetic particle precipitation. Instead, polar Es layer variability may involve both high‐latitude electrodynamic forcing and neutral‐atmospheric dynamics. Disturbance electric fields may modify metallic‐ion transport and convergence, whereas tidal winds regulate the wind‐shear conditions favorable for Es layer formation.