Three‐dimensional structure of ionospheric currents 1. Currents caused by diurnal tidal winds

Three‐dimensional current structure in the ionosphere (90–400 km) is calculated for (1,−2) tidal winds, assuming that the parallel conductivity (σ 0 ) is infinite and therefore that the electrostatic potential is constant along magnetic field line. Calculated structure of height‐integrated currents is essentially the same as the observed Sq current system. It is also shown that a meridional current system always exists in the equatorial region and that the east‐west component of currents could be reversed only near the equator. Though electric currents flow mainly in the E region, currents in the F region contribute a little, especially to poleward currents at middle and high latitudes.