Field‐aligned currents between conjugate hemispheres

Abstract

Interhemispheric field‐aligned currents flowing between dayside conjugate ionospheres are calculated for different seasons. The currents are a result of redistribution of original three‐dimensional currents because of different ionospheric conductivity in dark and sunlit conjugate hemispheres. Interhemispheric currents and related patterns for the electric potential distribution are computed for a reasonable model of the ionospheric conductivity. The interhemispheric field‐aligned currents are attached to the terminator position, and they close a part of ionospheric currents, flowing in the summer high‐latitude ionosphere, through the conjugate ionosphere of the opposite hemisphere. Although the interhemispheric currents are more significant for summer/winter conditions, they can be observed for equinoctial conditions as well because of a diurnal variation in the terminator position with respect to the geomagnetic poles. Interhemispheric currents in the winter ionosphere are generated mainly by sources in the summer hemisphere. An interesting consequence of the existence of interhemispheric currents is that auroral events can be observed not in the hemisphere with incident field‐aligned currents from a magnetospheric source but in the opposite hemisphere.