Solar cycle variations in the ionospheric Alfven resonator 1985-1995

Based on long-term observations of the resonance structure in the electroma gnetic background noise spectrum (resonance spectrum structure, RSS), recor ded in the frequency range 0.1-10 Hz over one complete solar cycle (11 year s, from 1985 to 1995), it was found that the resonance conditions for Alfve n waves in the ionosphere (ionospheric Alfven resonator) are determined at midlatitudes by the level of solar activity. RSS are regularly observed in years of minimum solar activity, and are practically absent in years of max imum solar activity. It is shown that consideration of the ionospheric Alfv en resonator explains the dependence of the RSS on solar activity. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.