First EISCAT measurement of electron-gas temperature in the artificially heated D-region ionosphere

The ionospheric electron gas can be heated artificially by a powerful radio wave. According to our modeling, the maximum effect of this heating occurs in the D-region where the electron temperature can increase by a factor of ten. Ionospheric plasma parameters such as N-e,T-e and T-i are measured by EISCAT incoherent scatter radar on a routine basis. However, in the D-regi on the incoherent scatter echo is very weak because of the low electron den sity. Moreover, the incoherent scatter spectrum from the D-region is of Lor entzian shape which gives less information than the spectrum from the E- an d F-regions. These make EISCAT measurements in the D-region difficult. A co mbined EISCAT VHF-radar and heating experiment was carried out in November 1998 with the aim to measure the electron temperature increase due to heati ng. In the experiment the heater was switched on/off at 5 minute intervals and the integration time of the radar was chosen synchronously with the hea ting cycle. A systematic difference in the measured autocorrelation functio ns was found between heated and unheated periods.