Electron concentration variations in the F1-region during magnetic storms in a low solar activity period

Vertical sensing data obtained with the help of DPS-4 digisondes in Irkutsk and Yakutsk are used to analyze the response of the F1-layer to magnetic disturbances in May 2005. It is found that the electron concentration is decreased at heights of 150–200 km during magnetic storms, and the amplitude of this negative disturbance increases with height. This effect is more distinct in Yakutsk than Irkutsk. The main gas constituents of the thermosphere during disturbed periods are estimated.