| Summary: | We analyzed the G condition occurrence, using data of ionospheric vertical sounding from stations Nbrilsk (69.4 degrees N, 88.1 degrees E), Irkutsk (52.5 degrees N, 104 degrees E) and.Hainan (18.3 degrees N, 109.3 degrees E) during the last extreme low solar activity period (2006-2009). In most cases, the three stations registered the G condition in May-August; in Norilsk, however, it was registered in March-April 2008. Under quiet geomagnetic conditions, the longest intervals (up to several hours) during which the G condition was continuously registered were observed in Irkutsk and Norilsk in June-July 2008. In Norilsk, it was registered almost every day in the morning and in the daytime (LT) during these months. We performed theoretical modeling of electron density distribution for the cases when the G condition was registered, taking into account the correction of the neutral atmosphere model. The obtained calculations are in good agreement with observed data. Besides, we showed that variations in thermospheric parameters (density, composition, temperature, and wind velocity) can promote formation of the G condition under quiet geomagnetic conditions during the last extreme low solar activity. (C) 2015 Elsevier Ltd. All rights reserved.
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