Solar wind dependence of the diurnal temperature variation in the thermosphere

Abstract

The ratio r = Tmax/Tmin of the maximum to the minimum exospheric temperature considered on a global scale was derived by means of static models using the densities obtained from the atmospheric drag of three low-inclination satellites. It is found that r varies with the solar cycle, lagging more than a year behind the variations of the 10.7-cm solar flux; on the other hand, the variations of r are in phase with , which is obtained by averaging the planetary geomagnetic index Kp over the whole year. The obvious conclusion is that, in the mechanism of the diurnal temperature variation in the thermosphere, the solar wind may be at least as important as, if not more important than, solar EUV. No appreciable lag is found in the variation of the minimum nighttime temperature when compared with the variations of the 10.7-cm solar flux.