Statistical characteristics of electromagnetic energy transfer between themagnetosphere, the ionosphere, and the thermosphere

We have determined, based on 28 days of European Incoherent Scatter Common Program I mode I data obtained between 1989 and 1991, statistical character istics of the energy-coupling processes between the lower thermosphere, ion osphere, and magnetosphere through an analysis of the electromagnetic energ y transfer rate J.E, the Joule heating rate J.E-1, and the mechanical energ y transfer rate U.(JxB) at altitudes of 125, 117, 109, and 101 km. At all a ltitudes the input electromagnetic energy is distributed to both Joule heat ing and mechanical energy. The energy distributed to Joule heating is large r than that to mechanical energy, but the latter is generally not negligibl e. All three rates respectively have two maxima, not in the midnight region but in the dawn and dusk. The enhancements of these rates have positive co rrelations with the increase of geomagnetic activity represented by the Kp index. The electromagnetic energy transfer rate is greatest at 117 km, beco ming smaller with decreasing altitude. It is mostly positive but can be neg ative. At 117 km the mechanical energy transfer rate is considerably smalle r than the electromagnetic energy transfer rate, suggesting that most of th e electromagnetic energy at this altitude is converted to Joule heating and a small portion of the electromagnetic energy goes to mechanical energy. A t 125 km the mechanical energy transfer rate is larger than that at 117 km. On average, 65% of the input electromagnetic energy is converted to Joule heating and 35% is converted to neutral mechanical energy. At 109 and 101 k m altitude the mechanical energy transfer rate becomes negative, hence the Joule heating rate is greater than the electromagnetic energy transfer rate , suggesting that not only electromagnetic energy but also mechanical energ y contribute to Joule heating.