Observations of changes in the bolometric contrast of sunspots

Details Observations of changes in the bolometric contrast of sunspots Observations of changes in the bolometric contrast of sunspots

Sep 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...432..403c&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 432, no. 1, p. 403-408

Astronomy and Astrophysics

Astronomy

39

Irradiance, Solar Radiation, Stellar Luminosity, Sunspots, Astronomical Photometry, Astronomical Satellites, Bolometers, Spaceborne Astronomy

Scientific paper

Rapid changes in the total solar irradiance from space borne sensors are largely due to the passage of large sunspots across the disk. The effect of sunspots has often been modeled, using ground-based observations, by the use of a sunspot index such as the PSI, which assumes that all sunspots have the same thermal structure, which remains constant with time. In this paper, we report on photometric observations of sunspot groups that show significant differences in their mean bolometric contrast ( up to a factor of 2) and some of which show cooling or warming during their disk transit. Most of these changes can be ascribed to the changing ratio of umbral-to-prenumbral area. By measuring the mean temperature or bolometric contrast, together with corrected (hemispherical) areas, we can determine the instantaneous solar luminosity fluctuation and its diurnal change due to individual sunspot groups. These results show that the use of solar indices based on estimates of sunspot area and fixed sunspot contrast, such as the photometric sunspot index, do not remove all of the significant sunspot effects from satellite measurements of the total solar irradiance.

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