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

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.