4. ELECTRON AND ION TEMPERATURES

The OETP instrument measured electron temperature while ORPA measured electron as well as the ion temperatures. Figure 12 shows profiles of median electron and ion temperatures from ORPA and it can be noted that the temperatures change little with SZA. The electron temperatures are about a factor of two higher than the ion temperatures, except for the antisolar region where the two are nearly equal. The observed temperatures have been explained by assuming adhoc topside heat fluxes or by reducing the thermal conductivity due to magnetic field fluctuations (see Nagy and Cravens, 1997, and references therein). Although one sees a large variability in the electron temperatures, most of this variability is in the ionopause region and follows changes in electron densities (Mahajan et al., 1994) as can be seen in Figure 13.

Fig.12:Plasma temperatures as measured by ORPA (a) elactron temparatures (b)
ion temperatures. There is little diurnal change in the temperatures. Ion temperature is about one half of the electron temperature, except in the antisolar region, where the two are equal ( from Miller et al., 1980).

Fig.13:Inverse correlation between the electron temperature and density in the ionosphere region.
The temprature in the main ionosphere remains nearly constant, while most of the variability is due to variatios in the ionopause region (from Mahajam et al., 1994).