As has been shown by observations from the Nimbus-7 and SMM satellites, the non-periodic, comparatively rapid decreases of the solar constant (to 0.25%) are mainly determined by the size and location of groups of sunspots passing through the Sun's central meridian. Variations of a quarter per cent are a rare enough occasion (occurring approximately once every two years). In the majority of cases, drops to 0.1% are noted.
The question of long-period (11-, 22-, and 80–90-year) variations of the astronomical solar constant (ASC) is still open to speculation. The four-year series of observations on Nimbus-7 indicates very definitely the presence of a maximum in smoothed ASC values in January of 1979, and the following permanent decrease in 1980–82 with the varying rate up to 0.05% annual.
The compiled by the authors temporal series of the ASC variability for the 1925–1980 period has been confirmed, in our opinion, experimentally. Obviously, the long-period variations must be associated not with the development of active areas, but with temperature changes in the non-perturbed photosphere. It is supposed that the temperature gradient variation in the photosphere in the 11-year cycle leads to the redistribution of radiation from various photospheric levels. As a result, the ASC varies quasi-periodically both within the cycle, and from one cycle to another. Since the phase variation of the ASC has been noted in some cycles (e.g., cycle No. 16), the existence of a component of another periodicity can be supposed. Solar activity variations are relevant to different kinds of solar radiation: from cosmic and X-rays to radiofrequency radiation. The combined influence of these emissions on the atmosphere apparently leads to a several times enhancement of small ASC variations (drops), probably by a factor of ten. The ‘enhancement’ of the solar radiation variation can be detected in the so-called meteorological solar constant (MSC). Analysis of experimental data has shown that at tropospheric levels the cyclic MSC variations can reach 4% (cycle No. 19). It should be noted that in the mid-latitude belt of the northern hemisphere the MSC changes occur in phase with the variation of the intensity of galactic cosmic rays.
The 22-year component in the ASC is considerably weaker than the 11-year component.
KeywordsSolar Radiation Solar Activity Gradient Variation Central Meridian Solar Constant
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