Morning Overshoot of Te Enhanced by Downward Plasma Drift in the Equatorial Topside Ionosphere

The morning overshoot in electron temperature, Te, which occurs in the sunlit atmosphere of low electron density during early morning hours, is a well known phenomenon. Studies of the phenomenon carried out using the Hinotori satellite observations reveal that the overshoot enhances in the topside equatorial F-region for a short period of time in the morning. The enhancement in the overshoot is found to depend on season and solar activity; it is strong during the northern summer months and grows with the increase in solar activity. Theoretical model calculations show that the enhancement in Te is caused by a reduction in electron density in the topside ionosphere due to a downward drift of plasma.