Transmission of Stormtime Electric Field and Currents to the Mid-Equatorial Latitude Ionosphere in the Magnetosphere-Ionosphere-Ground Circuit

Abstract:

Three kinds of dynamos are activated in the magnetosphere during geomagnetic storms, which supply the electric field and currents to the mid-equatorial ionosphere. At the onset of the storm, the solar wind shock activates the dynamo of the dawn-to-dusk electric field and Region-1 field-aligned currents for several to ten min, which transmit to the equatorial ionosphere and intensify the equatorial electrojet (EEJ). During the storm main phase, the southward interplanetary magnetic field (IMF) activates the dynamo of the dawn-to-dusk electric field and the R1 FACs for several hours, which develop the ring current and intensify the EEJ. During the storm recovery phase, on the other hand, the electric field and currents reverse their direction, prohibit the ring current from developing and cause the counterelectrojet in the equatorial ionosphere (CEJ). The CEJs are often observed even during the storm main phase under the relatively constant southward IMF. The long-lasting CEJs are superimposed by large amplitude impulsive/irregular CEJs. We have detected the stormtime electric fields in midlatitude with the SuperDARN radar and HF Doppler sounder in Japan during the stormtime CEJs. The long-lasting CEJs should be caused by the thermospheric wind dynamo (disturbance dynamo), but the impulsive/irregular CEJs are found to be caused by substorms as well as by convection reductions. The transmission of the electric field and currents from the magnetospheric dynamos to the mid-equatorial latitude ionosphere is explained by means of the magnetosphere-ionosphere-ground (MIG) transmission line developed by Kikuchi [JGR 2014]. The Poynting flux is transmitted to the polar ionosphere by the Alfven waves in the magnetosphere-ionosphere (MI) transmission line and by the TM0 (TEM) mode waves to the mid-equatorial ionosphere in the Earth-ionosphere waveguide (ionosphere-ground (IG) transmission line). A fraction of the Poynting flux in the IG transmission line leaks into the ionosphere, driving the ionospheric currents in the E-region and motion of plasma in the F-region. Thus, the midlatitude electric field and equatorial currents are well correlated.