Auroral absorption and electric fields in the magnetosphere

Using the observations on Kotel'nyi Island, Tiksi, and Zhigansk, the annual and diurnal variations in the occurrence frequency of the auroral absorption and their relation to the interplanetary magnetic field (IMF) are studied. Two types of variations in the auroral absorption, one of which is independent of and another dependent on the IMF, have been distinguished. The possible sources of these variations are discussed. The IMF-independent variation is caused by a change in the relative position of the planes of the magnetospheric plasma sheet and geomagnetic equator; the IMF-dependent variation, by the penetration of the solar-wind electric field into the magnetosphere.