151-153The thermal structure of the equatorial topside ionosphere is theoretically investigated to explain the experimentally observed features, viz. (i) isothermal region in the 400-500 km range, (ii) close coupling of electron and ion temperatures, and (iii) lower temperatures compared to mid-latitudes. The main reasons for these features seem to be the larger electron densities in the 400-500 km range and the absence of protonospheric heat flux flowing into the topside ionosphere. The theoretical profiles, calculated on the above basis, are found to be in good agreement with the experimentally observed profiles in the 400-1000 km region
