Field-aligned currents between conjugate hemispheres

Interhemispheric field-aligned currents flowing between dayside conjugate i onospheres are calculated for different seasons. The currents are a result of redistribution of original three-dimensional currents because of differe nt ionospheric conductivity in dark and sunlit conjugate hemispheres. Inter hemispheric currents and related patterns for the electric potential distri bution 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 su mmer high-latitude ionosphere, through the conjugate ionosphere of the oppo site hemisphere. Although the interhemispheric currents are more significan t for summer/winter conditions, they can be observed for equinoctial condit ions 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 int eresting consequence of the existence of interhemispheric currents is that auroral events can be observed not in the hemisphere with incident field-al igned currents from a magnetospheric source but in the opposite hemisphere.