Nighttime Midlatitude E-F Coupling in Geomagnetic Conjugate Ionospheres: A Double Thin Shell Model and a Multi-Source Data Investigation

Abstract

Abstract Geomagnetic conjugate mid‐latitude nighttime ionospheres are frequently simultaneously populated with electrified nighttime medium‐scale traveling ionospheric disturbances (MSTIDs). Earlier observations and theoretical analysis have underscored the ionosphere E‐F coupling and the postulation of coupled conjugate hemispheres, playing a pivotal role in the formation of electrified MSTIDs. In this paper, the conjugate MSTIDs are studied to elucidate the causes and effects of E‐F coupling in the interhemispheric coupled ionosphere. The hemisphere‐coupled ionospheres over Japan and Australia are observed and analyzed using total electron content (TEC) measurements, supplemented with multi‐source observations from ionosondes, Ionospheric Connection Explorer (neutral wind), Constellation Observing System for Meteorology, Ionosphere, and Climate (electron density), and Swarm (magnetic field). A double‐thin‐shell model is introduced to analyze the ionospheric responses in E and F regions during the coupling process. For the first time, observation results provide the evidence that F‐region geomagnetic conjugate irregularities in both hemispheres are mainly driven by the Es layers in the summer hemisphere. The Es layer in the summer hemisphere subsequently triggers local E‐F coupling and inter‐hemispheric coupling. In the winter hemisphere, Es layers show amplitude reduction or even dissipation during the interhemispheric coupling process. Furthermore, thermospheric winds, non‐equipotential magnetic field lines, and background TEC are presumed candidates for the inter‐hemispheric asymmetry in MSTIDs amplitudes and growth rates.