Formation of negative disturbances in the topside ionosphere during solar flares

Abstract

[1] The results of studies of the ionospheric response to solar flares are presented. The results are based on the observations of GPS signals and at incoherent scatter radars and on theoretical calculations. Analyzing the GPS data, the method based on a partial “shadowing” of the atmosphere by the Earth was used. This method made it possible to estimate the value of the electron content variations in the topside ionosphere during the solar flare on 14 July 2000. We obtained that according to the GPS data at altitudes of the topside ionosphere (h > 300 km) a flare is able to cause a decrease of the electron content. Similar eects of formation of a negative disturbance in the ionospheric region were observed also during the solar flares on 21 and 23 May 1967 by the Arecibo radar. Using the theoretical model of ionosphere‐plasmasphere interaction, we study in this paper the mechanism of formation of negative disturbances in the topside ionosphere during solar flares. It is shown that the intense transport of O + ions into the above-situated plasma caused by a sharp increase in the ion production rate and thermal expansion of the ionospheric plasma is a cause of the formation of the negative disturbance in the electron concentration in the topside ionosphere. INDEX TERMS: 2481 Ionosphere: Topside ionosphere; 2435 Ionosphere: Ionospheric disturbances; 2467 Ionosphere: Plasma temperature and density; KEYWORDS: Electron content variations; solar flare; GPS receivers network; Arecibo IS installation.