Sunspot cycle variations of ensemble-averaged active regions

Abstract

We examine published sunspot and calcium plage areas for 1620 solar active regions between 1974 and 1985. With these data we study the properties of ensemble-averaged active regions. The average sunspot area per region, the average plage to sunspot area ratio, and the average plage intensity of regions all vary significantly with the sunspot cycle and in correlation with one another. The average plage area per region varies significantly but is uncorrelated with the sunspot cycle and with the other quantities. While the plage and sunspot areas and the plage intensities of individual active regions observed over a two-year period are strongly correlated, the relationship among these quantities appears to change over an 11-yr period. These results suggest the existence of some energetic connection between active region sunspot areas and plage intensities. Further, if energy balance between sunspot luminosity deficits and facular luminosity excesses holds, then standard models relating these quantities to sunspot and plage areas will have to be modified. Overall energy balance can neither be established nor ruled out.

Excess facular emission from an isolated active region during solar minimum: the example of NOAA AR 7978

“…Again, the greatest excess related to the quiet Sun background occurs at the shortest wavelength (402 nm). The wavelength dependence observed in this example is similar to the spectrum for faculae reported in earlier studies (Chapman and McGuire, 1977;Lawrence, 1987) and from theoretical models (Unruh et al, 1999). There is no signiÿ-cant change in the wavelength dependence with the age of the AR.…”

Deriving effective sunspot temperatures from SOHO/VIRGO irradiance measurements

“…But still, the classical photometric starspot models are not applicable to the solar light curves for two reasons: 1) The brightening effect of faculae has not yet been included in the starspot models. However, the effect of faculae is known to be comparable and sometimes even larger than the darkening effect of sunspots (Chapman 1984;Chapman et al 1982Chapman et al , 1992Lawrence 1987;Foukal & Lean 1988;Steinegger et al 1996). 2) There is morphological evolution of sunspots.…”

“…For the Sun, the effect of faculae is known to be comparable and sometimes even larger than the darkening effect of sunspots (Chapman 1984;Chapman et al 1982Chapman et al , 1992Lawrence 1987;Foukal & Lean 1988;Steinegger et al 1996). Faculae have zero or negligible contrast at or near the disk center.…”

Observations of Photospheric Dynamics and Magnetic Fields: From Large-Scale to Small-Scale Flows

“…It also has an impact on sunspot models. Along the same line, Lawrence (1987) has studied various properties of active regions over the solar cycle, such as average sunspot area per region, average plage to sunspot area ratio, and average plage intensity. They all vary during the cycle, suggesting the existence of some strong connection between active region sunspot areas and plage intensities, with some influence on the models relating sunspot and plage luminosities.…”