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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.

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We present Akebono observations of the polar wind velocity and the ambient electron temperature in the polar ionosphere. The velocity of the H+ polar wind increases from about 1 km/s at 2000 km altitude to about 6 km/s at 4000 km altitude, and correlates with the local electron temperature at a given altitude. It is only weakly dependent on magnetic activity, but is generally more variable at active times. Our observation demonstrates the direct relationship between the local magnitude of ion acceleration and that of the ambipolar electric field responsible for the acceleration.