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 absorpti on and their relation to the interplanetary magnetic field (IMF) are studie d. Two types of variations in the auroral absorption, one of which is indep endent of and another dependent on the IMF, have been distinguished. The po ssible sources of these variations are discussed. The IMF-independent varia tion is caused by a change in the relative position of the planes of the ma gnetospheric plasma sheet and geomagnetic equator; the IMF-dependent variat ion, by the penetration of the solar-wind electric field into the magnetosp here.