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Observations of changes in the bolometric contrast of sunspotsRapid 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.
Document ID
19950040787
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Chapman, G. A.
(San Fernando Observatory, California State Univ. Northridge, CA, United States)
Cookson, A. M.
(San Fernando Observatory, California State Univ. Northridge, CA, United States)
Dobias, J. J.
(San Fernando Observatory, California State Univ. Northridge, CA, United States)
Date Acquired
August 16, 2013
Publication Date
September 1, 1994
Publication Information
Publication: Astrophysical Journal, Part 1
Volume: 432
Issue: 1
ISSN: 0004-637X
Subject Category
Solar Physics
Accession Number
95A72386
Funding Number(s)
CONTRACT_GRANT: NSF ATM-91-15111
CONTRACT_GRANT: NSF ATM-88-17634
CONTRACT_GRANT: NASW-3017
Distribution Limits
Public
Copyright
Other

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