Solar limb photometry data obtained in 1990 shows a decline in the active region facular contribution to the solar irradiance from the previous year - in accord with the maximum in the sunspot cycle occurring in late 1989. In contrast, the nonfacular and nonsunspot contribution to the solar flux increased compared to 1989. This third component of the irradiance variation is consistent with a significant increase in the total mean solar irradiance from the value observed near the time of sunspot maximum. Evidently, the irradiance maximum, like other solar activity indices, exhibits a phase lag with respect to the solar activity maximum as measured by the sunspot number.
No takes yet. Share an insight, caveat, or question.
Kuhn et al. (1991) studied this question.