Solar total irradiance and sunspot area in 1981

Precise observations of the total solar irradiance in 1980 from the Solar Maximum Mission showed a strong correlation with the projected total sunspot area. This correlation “explained” about half of the variance (r ～ 0.75) in the total-irradiance data, leaving the other half for other solar phenomena and errors in the data. We have now begun the analysis of the intervening three years of “spin-mode” data, which have reduced coverage. We find that the correlation persists at about the same qualitative level, but with increased scatter that can be attributed to the smaller amount of data. The flatness of the distribution of areas of sunspot groups makes it possible to estimate PSI approximately from only the large groups.