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

Short-term changes of electron concentration in the ionospheric F-region have been studied during a campaign of rapid sequence vertical ionospheric sounding. The wave-like structures occurred under low solar and geomagnetic activity. The most probable source of the observed waves was below the 175 km level and probably not in the auroral zone. The vertical components of propagation characteristics of the observed waves correspond to the theory of acoustic gravity wave propagation in the ionosphere and confirm the position of the source being below the studied heights. Another case studied showed the effects of passage of strong tropospheric cold front under high solar activity during February 1990. (C) 2001 Elsevier Science Ltd. All rights reserved.