Sunspot irradiance deficit, facular excess, and the energy balance of solar active regions.

Details Sunspot irradiance deficit, facular excess, and the energy balance of solar active regions. Sunspot irradiance deficit, facular excess, and the energy balance of solar active regions.

Jun 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996a%26a...310..635s&link_type=abstract

Astronomy and Astrophysics, v.310, p.635-645

Astronomy and Astrophysics

Astrophysics

27

Sun: General, Activity, Faculae, Sunspots

Scientific paper

Plage areas and intensities derived from CaIIK spectroheliograms are used as a proxy for the facular irradiance excess of solar active regions for the period 19 August to 4 September 1980. Applying a calibration method proposed by Vrsnak et al. (1991) and adopting it for photometrically measured plage intensities, the "Photospheric Facular Index" with constant facular contrast C_P_=0.0185 is replaced by a scheme of variable C_P_, depending on the plage brightness. An increase of C_P_ from 0.015 to =~0.025 is found for plage areas varying from a few tens to approx. 6000 millionths of solar hemispheres (μh). Combining the facular irradiance excess with sunspot deficits (as determined for the same period by Steinegger et al. 1990) yields good agreement with the irradiance variations measured by SMM/ACRIM, using a center-to-limb variation of C_P_ according to Chapman & Meyer (1986). For 60 active regions out of this period, the luminosity ratio of facular excess to sunspot deficit decreases from about 4 for regions with sunspot areas of 30μh to =~0.4 for sunspots of areas >1000μh. Additionally, we find a decrease of the plage to sunspot area ratio from about 30 for small spots with areas around 30μh to 3 for spots larger than 1000μh.

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