Panel Discussions on Total Solar Irradiance Variations and the Maunder Minimum

Abstract

For more than a decade, total solar irradiance has been monitored from several satellites, namely the Nimbus-7, Solar Maximum Mission (SMM), the NASA ERBS, NOAA9 and NOAA1O, EURECA, and the Upper Atmospheric Research Satellite (UARS) (e.g. Willson and Hudson, 1991; Hoyt et al., 1992; Mecherikunnel et al., 1988; Romero et al., 1994). These observations have revealed variations in total irradiance ranging from minutes to the 11-year solar cycle (Figure 1, from Frohlich 1994). The very small, rapid irradiance fluctuations are due to solar oscillations (Woodard and Hudson, 1983; Frohlich, 1992). The short-term variations (from days to months) are directly related to the evolution of active regions via the combined effect of dark sunspots and bright faculae (Chapman, 1987). The most important discovery of irradiance observations is the 0.1% peak-to-peak variation in total solar irradiance over the solax cycle (Willson and Hudson, 1991). This solar-cycle-related variation of total irradiance is attributed to the changing emission of bright magnetic elements, including faculae and the magnetic network (Foukal and Lean 1988). This solar cycle variability may also be related to changes in the photospheric temperature; however it is not clear as yet whether this change can be linked to the bright network component (Kuhn et al., 1988).