Extension of the F10.7 Index to 1905 using Mt. Wilson Ca K Spectroheliograms

Foukal, P.

doi:10.1029/98gl02057

Cited by 33 publications

(26 citation statements)

References 11 publications

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“…So a stable and straightforwardly derivable relationship holds up to moderate activity levels. Demonstration of this simple relationship over the 1916-1976 period of overlap between the two time series was not possible before the digitization and reduction of the Ca K spectroheliograms (Foukal 1998a;Tlatov et al 2009;Bertello et al 2010). But (1) underestimates the observed A pn in cycles 18 and 19 by about a factor 2.…”

Section: The Statistical Relationship Between Areas Of Wl Faculae Andmentioning

confidence: 99%

“…Several factors might, in principle, contribute to this underestimate. For one, A pn includes not only the active region plages but also the surrounding active network (Foukal 1998a). But A f also includes the active network.…”

Section: The Statistical Relationship Between Areas Of Wl Faculae Andmentioning

confidence: 99%

“…Wilson Observatory (MWO) and Sacramento Peak Observatory spectroheliograms (Foukal 1998a;Foukal et al 2009) for the years 1916-1999. The relative variation of annual mean A pn agrees with independent digitization and analysis of the MWO plates by Bertello et al (2010) and with R.…”

Section: The Statistical Relationship Between Areas Of Wl Faculae Andmentioning

confidence: 99%

“…Its use has been largely justified by the good correspondence between smoothed values of R and chromospheric proxies like F10.7 (e.g., Foukal & Lean 1990;Foukal 1998a), which can be understood given the loose tendency of plages to accompany spots. But the main reason for its use is the length of the record of R. Spots have been recorded on a regular basis for much longer than have plages or faculae.…”

Section: Introductionmentioning

confidence: 99%

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Dimming of the Mid-20th Century Sun

Foukal

2015

ApJ

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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.

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Section: The Statistical Relationship Between Areas Of Wl Faculae Andmentioning

confidence: 99%

Section: The Statistical Relationship Between Areas Of Wl Faculae Andmentioning

confidence: 99%

Section: The Statistical Relationship Between Areas Of Wl Faculae Andmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Dimming of the Mid-20th Century Sun

Foukal

2015

ApJ

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“…This data set was kindly provided by P. Foukal. Areas were measured from spectroheliograms and photoheliograms in the K line of Ca II obtained at Mount Wilson, McMath‐Hulbert and Big Bear observatories in the period 1915–1984 [ Foukal , 1996, 1998]. Later, this time series was extended until 1999 using data from Sacramento Peak Observatory (SPO).…”

Section: An Example Of Errors Introduced By An Uncritical Use Of Uncamentioning

confidence: 99%

A homogeneous database of sunspot areas covering more than 130 years

et al. 2009

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[1] The historical record of sunspot areas is a valuable and widely used proxy of solar activity and variability. The Royal Greenwich Observatory regularly measured this and other parameters between 1874 and 1976. After that time records from a number of different observatories are available. These, however, show systematic differences and often have significant gaps. Our goal is to obtain a uniform and complete sunspot area time series by combining different data sets. A homogeneous composite of sunspot areas is essential for different applications in solar physics, among others for irradiance reconstructions. Data recorded simultaneously at different observatories are statistically compared in order to determine the intercalibration factors. Using these data we compile a complete and cross-calibrated time series. The Greenwich data set is used as a basis until 1976, the Russian data (a compilation of observations made at stations in the former USSR) are used between 1977 and 1985, and data compiled by the USAF network are used since 1986. Other data sets (Rome, Yunnan, and Catania) are used to fill up the remaining gaps. Using the final sunspot areas record the Photometric Sunspot Index is calculated. We also show that the use of uncalibrated sunspot areas data sets can seriously affect the estimate of irradiance variations. Our analysis implies that there is no basis for the claim that UV irradiance variations have a much smaller influence on climate than total solar irradiance variations.

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Short Term, Direct Indices of Solar Variability

Lean¹

2000

Solar Variability and Climate

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Extension of the F10.7 Index to 1905 using Mt. Wilson Ca K Spectroheliograms

Cited by 33 publications

References 11 publications

Dimming of the Mid-20th Century Sun

Dimming of the Mid-20th Century Sun

A homogeneous database of sunspot areas covering more than 130 years

Short Term, Direct Indices of Solar Variability

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