Height-dependent energy exchange rates in the high-latitude E region ionosphere

The statistical properties of the altitude profiles of the different energy transfer rates in the auroral ionosphere are studied by using the European Incoherent Scatter radar measurements in TromsO (67 degrees cgmLat). Aikio et al. (2012) found that during active conditions, winds reduce the height-integrated Joule heating rates in the evening but enhance them in the morning. Here we show that the reduction in the evening takes place close to and above the peak altitude of Joule heating, so that the Joule heating peak descends from the Pedersen conductivity maximum at 120 km down to about 115 km. Values close to the peak are reduced also in the morning, but the positive effect by winds above the peak makes the net effect positive. The altitude range where the electromagnetic energy of magnetospheric origin is converted to the mechanical energy of the neutrals is only 20-35km wide in the E region and shows a clear magnetic local time variation. Model calculations are made to study the effect of the angle between the wind and electric field directions on the energy transfer rates and to explain the observed features.