Salient Midlatitude Ionosphere‐Thermosphere Disturbances Associated With SAPS During a Minor but Geo‐Effective Storm at Deep Solar Minimum

Abstract

AbstractThis work conducts a focused study of subauroral ion‐neutral coupling processes and midlatitude ionospheric/thermospheric responses in North America during a minor but quite geo‐effective storm on September 27–28, 2019 under deep solar minimum conditions. Several prominent storm‐time disturbances and associated electrodynamics/dynamics were identified and comprehensively analyzed using Millstone Hill and Poker Flat incoherent scatter radar measurements, Fabry‐Perot interferometer data, total electron content data from Global Navigation Satellite System observations, and thermospheric composition O/N2 data from the Global‐scale Observations of Limb and Disk mission. Despite solar minimum conditions, this minor storm produced several prominent dynamic features, in particular (a) Intense subauroral polarization stream (SAPS) of 1,000 m/s, overlapping with a deepened main trough structure. (b) An enhanced westward wind of 230 m/s and a significant poleward wind surge of 85 m/s occurred in the post‐SAPS period. (c) Large‐scale traveling ionospheric disturbances (TIDs) were generated and propagated equatorward across mid‐latitudes in the storm main phase. TID characteristics were significantly affected by SAPS, evolving into divergent propagation patterns. (d) SAPS was situated on the poleward edge of a considerable storm‐enhanced density structure. (e) The midlatitude ionosphere and thermosphere exhibited a prolonged positive storm effect in the main phase and beginning of recovery phase, with 5–10 TECU increase and 10%–30% O/N2 enhancement for 12 h. This was followed by a considerable negative storm effect with 5–10 TECU and 20%–40% O/N2 decrease. Results show that minor storm intervals can produce substantial mid‐latitude ionospheric and thermospheric dynamics in low solar flux conditions.