A THEORY OF THERMOSPHERIC DYNAMICS .2. GEOMAGNETIC ACTIVITY EFFECT, 27-DAY VARIATION AND SEMIANNUAL VARIATION

The geomagnetic activity effect, the 27-day variation and the semiannual variation of the thermospheric density are nearly independent of local time. Therefore, they are treated by a one dimensional model in order to find out the height distribution and the amount of energy necessary to create the observed amplitudes and phases of the neutral density between 120 and 400 km altitude. Three types of heat energy sources have been considered which simulate energy input: I at the bottom of the thermosphere; II within the thermosphere; and III at the top of the thermosphere. The geomagnetic activity effect and the 27-day variation can be described as generated by heat source II which is interpreted as resulting from corpuscular radiation into the aurora zones and from solar active region EUV radiation, respectively. The semiannual effect can be described by heat source I and is interpreted as resulting from dissipated energy of a tidal wave from the lower atmosphere. The leakage of the energy of this tidal wave into the thermosphere shows a semiannual variation which creates the observed density variations. Quantitative calculations give the amount of energy of the various heat sources, amplitudes and phases of the generated density and temperature variations and their dependence on solar activity. © 1969.