DIMMING OF THE MID-20TH CENTURY SUN

Journal Article · Thu Dec 10 04:00:00 EST 2015 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/815/1/9· OSTI ID:22521823

Foukal, Peter ^[1]

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1. 192 Willow Rd., Nahant, MA 01908 (United States)

Area changes of photospheric faculae associated with magnetic active regions are responsible for the bright contribution to variation in total solar irradiance (TSI). Yet, the 102-year white light (WL) facular record measured by the Royal Greenwich Observatory between 1874 and 1976 has been largely overlooked in past TSI reconstructions. We show that it may offer a better measure of the brightening than presently used chromospheric proxies or the sunspot number. These are, to varying degrees, based on magnetic structures that are dark at the photosphere even near the limb. The increased contribution of the dark component to these proxies at high activity leads to an overestimate of solar brightening around peaks of the large spot cycles 18 and 19. The WL facular areas measure only the bright contribution. Our reconstruction based on these facular areas indicates that TSI decreased by about 0.1% during these two cycles to a 20th century minimum, rather than brightening to some of the highest TSI levels in four centuries, as reported in previous reconstructions. This TSI decrease may have contributed more to climate cooling between the 1940s and 1960s than present modeling indicates. Our finding adds to previous evidence that such suppression of solar brightening by an increased area of dark flux tubes might explain why the Sun is anomalously quiet photometrically compared to other late-type stars. Our findings do not change the evidence against solar driving of climate warming since the 1970s.

• OSTI ID: 22521823
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 815; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
CLIMATES
COMPARATIVE EVALUATIONS
COOLING
FACULAE
PHOTOMETRY
PHOTOSPHERE
RADIANT FLUX DENSITY
SUN
SUNSPOTS
TUBES
VARIATIONS
VISIBLE RADIATION