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.