Theoretical models for the solar-cycle variation of the upper atmosphere

Models of the upper atmosphere for different levels of solar activity have been calculated by solving the heat conduction equation under quasi-hydrostatic conditions by means of the procedure described in detail in a previous paper. In these calculations the fluxes of both heat sources (EUV and corpuscular heat source) are varied in proportion to the long term averages of the 10.7-cm solar fluxes in order to account for different levels of solar activity during the solar cycle. The resulting temperatures of the exosphere can be represented by Tmin = 4.5 · S + 275 (°K) and Tmax = 7.1 · S + 372 (°K) where Tmin and Tmax are the diurnal minimum and maximum temperatures respectively, and S is the monthly average of the 10.7-cm solar flux in units of 10−22 w/m2 cps. The slope for Tmin is in good agreement with that found by L. G. Jacchia from analysis of satellite drag. In this paper the physical properties (temperature, density, scale height, and mean molecular weight) are illustrated as functions of local time and of altitudes between 120 and 2050 km for five different values of S.