부산대학교 도서관

The physical properties of the upper atmosphere are determined mainly by heat conduction, the heat sources, and the barometric law. An analysis of the integro-differential equation that describes these physical processes is carried out. It is found that heating of the thermosphere by absorption of the solar extreme ultraviolet (EUV) radiation alone cannot explain the observed diurnal variation of density and temperature, since this absorption yields maximum of these properties at about 17: 00 local time, instead of 14: 00 where it is observed. Secondly, if the EUV flux is adjusted to give the observed average temperature, then the diurnal variation in density is much too large compared with the observed amplitude. Further, this model requires an extremely high efficiency for the conversion of EUV radiation into heat, if the required flux is compared with measurements of the EUV flux. Thus, it is necessary to have another heat source in addition to the heating from absorption of EUV radiation. If an additional heat source is used, which has a maximum at about 9:00 local time and a flux of 1 erg cm/sup -2/sec/sup -1/, a time -dependent model of the upper atmosphere is obtained that is in agreement with the observed densities. There is evidence that this additional heat source derives its energy ultimately from the solar corpuscular radiation. The resuits of calculations for a model in the equatorial and temperature zones of the earth are presented, for those times when the average solar activity corresponds to a solar radiation flux of 200 x 10/ sup -23/ wm/sup -2/(cps)/sup -1/ at 10.7-cm wavelength. The physical properties (temperature, density, pressure, scale height, mean molecular weight, and the number densities of N/sub 2/, O/sub 2/, O, He, and H) are given as a function of local time for altitudes between 120 and 2050 km. (auth)