Tropospheric events and possible related gravity wave activity effects on the ionosphere

Short-term changes of electron concentration in the ionospheric F-region ha ve been studied during a campaign of rapid sequence vertical ionospheric so unding. The wave-like structures occurred under low solar and geomagnetic a ctivity. The most probable source of the observed waves was below the 175 k m level and probably not in the auroral zone. The vertical components of pr opagation characteristics of the observed waves correspond to the theory of acoustic gravity wave propagation in the ionosphere and confirm the positi on of the source being below the studied heights. Another case studied show ed the effects of passage of strong tropospheric cold front under high sola r activity during February 1990. (C) 2001 Elsevier Science Ltd. All rights reserved.