EISCAT UHF studies of ionospheric currents on June 16-17, 1987

The first E-region density estimates have been derived at 4 different heights (101, 109, 119 and 132 km), by the EISCAT CP-1 tristatic experiment. The currents at daytime are found to be driven by the neutral wind and by the electric field during a disturbed event during nighttime. The height integrated currents do agree reasonably well with the magnetic field fluctuations observed by a nearby magnetometer. The eastward component of the current does however agree better with the variations in the H-component than does the northward component of the current with its corresponding D-component. This is probably due to a stronger dominance of the Pedersen current connected to field aligned currents in the meridional direction. The Harang discontinuity is found to be related to a westward component of the electric field and a particle precipitation with root mean square energies of 5 keV. The Joule and particle heating rates are found to be comparable, but as the Joule heating takes place at higher altitudes where the density of the neutral atmosphere is smaller it is expected that the Joule heating will have a greater effect in the ionosphere.