Dimming of the Mid-20th Century Sun

Foukal, P.

doi:10.1088/0004-637x/815/1/9

Cited by 6 publications

(11 citation statements)

References 40 publications

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“…Although on average the brightness increases after restoration, the fraction of negative contrast pixels at these magnetic flux ranges is more than 50%, thus suggesting a different temperature stratification than pixels characterized by a positive contrast. If, as suggested in Foukal (2015) (see also Foukal 1993;Foukal et al 1990), the coverage of such features increases with the activity, then available reconstruction techniques making use of facular coverage as derived by chromospheric emission (e.g. Lean 2000;Foukal 2012) overestimate the contribution of faculae to irradiance, especially during the strongest cycles.…”

Section: Implications For Solar Irradiance Studiesmentioning

confidence: 98%

Photometric Properties of Network and Faculae Derived from HMI Data Compensated for Scattered Light

Criscuoli

Norton

Whitney

2017

ApJ

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We report on the photometric properties of faculae and network as observed in full-disk, scattered-light corrected images from the Helioseismic Magnetic Imager. We use a Lucy-Richardson deconvolution routine that corrects an image in less than one second. Faculae are distinguished from network through proximity to active regions. This is the first report that full-disk observations, including center-tolimb variations, reproduce the photometric properties of faculae and network observed previously only in sub-arcsecond resolution, small field-of-view studies, i.e. that network, as defined by distance from active regions, exhibit higher photometric contrasts. Specifically, for magnetic flux values larger than approximately 300 G, the network is brighter than faculae and the contrast differences increases toward the limb, where the network contrast is about twice the facular one. For lower magnetic flux values, network appear darker than faculae. Contrary to reports from previous full-disk observations, we also found that network exhibits a higher center-to-limb variation. Our results are in agreement with reports from simulations that indicate magnetic flux alone is a poor proxy of the photometric properties of magnetic features. We estimate that the contribution of faculae and network to Total Solar Irradiance variability of the current Cycle 24 is overestimated by at least 11% due to the photometric properties of network and faculae not being recognized as different. This estimate is specific to the method employed in this study to reconstruct irradiance variations, so caution should be paid when extending it to other techniques.

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Section: Implications For Solar Irradiance Studiesmentioning

confidence: 98%

Photometric Properties of Network and Faculae Derived from HMI Data Compensated for Scattered Light

Criscuoli

Norton

Whitney

2017

ApJ

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“…This suggests that at least some of the global warming from the 1970s to 2000 could have been due to increasing TSI, i.e., contradicting a key implication of Foukal (2012). The modified Foukal (2015) reconstruction is even more distinct. It implies that TSI reached an initial peak in the late 1930s, before declining until 1958, and then increasing to a maximum in 2000.…”

Section: Implications Of the Satellite Era Debate For Presatellite Er...mentioning

confidence: 98%

“…Over the years, several researchers have identified several time series from the records of solar observers that seem to be capturing different aspects of solar variability than the basic sunspot numbers [24,[179][180][181][182][183][184][185]. Examples include the average umbral/penumbral ratio of sunspots [181], the length of sunspot cycles [49,68,182,183,[186][187][188][189], solar rotation rates [184], the "envelope" of sunspot numbers [185], variability in the 10.7cm solar microwave emissions [65,190], solar plage areas (e.g., from Ca II K spectroheliograms) [190][191][192][193], polar faculae [61,62,194], and white-light faculae areas [195,196]. Another related sunspot proxy that might be useful is the sunspot decay rate.…”

Section: Implications Of the Satellite Era Debate For Presatellite Er...mentioning

confidence: 99%

“…Foukal (2012) [193] and Foukal (2015) [196] used a similar approach to the Wang et al (2005) [172] reconstruction but used slightly different solar proxies for the 20 th century presatellite era. Foukal (2012) used 10.7cm solar microwave emissions for the 1947-1979 period and solar plage areas (from Ca II K spectroheliograms) for the 1916-1946 period.…”

Section: Implications Of the Satellite Era Debate For Presatellite Er...mentioning

confidence: 99%

“…Examples of different TSI reconstructions that can be created by varying the choice of solar proxies used for the pre-satellite era and the choice of TSI composite used for the satellite era. The Foukal (2012Foukal ( , 2015 [193,196] series using PMOD were downloaded from http://heliophysics.com/solardata.shtml (Accessed 20/06/2020). The equivalent ACRIM series were rescaled using the annual means of the ACRIM TSI composite which was downloaded from http://www.acrim.com/Data%20Products.htm (Accessed 01/07/2020).…”

Section: Implications Of the Satellite Era Debate For Presatellite Er...mentioning

confidence: 99%

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How much has the Sun influenced Northern Hemisphere temperature trends? An ongoing debate

Connolly¹,

Soon²,

Connolly³

et al. 2021

Res. Astron. Astrophys.

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In order to evaluate how much Total Solar Irradiance (TSI) has influenced Northern Hemisphere surface air temperature trends, it is important to have reliable estimates of both quantities. Sixteen different estimates of the changes in TSI since at least the 19th century were compiled from the literature. Half of these estimates are “low variability” and half are “high variability”. Meanwhile, five largely-independent methods for estimating Northern Hemisphere temperature trends were evaluated using: 1) only rural weather stations; 2) all available stations whether urban or rural (the standard approach); 3) only sea surface temperatures; 4) tree-ring widths as temperature proxies; 5) glacier length records as temperature proxies. The standard estimates which use urban as well as rural stations were somewhat anomalous as they implied a much greater warming in recent decades than the other estimates, suggesting that urbanization bias might still be a problem in current global temperature datasets – despite the conclusions of some earlier studies. Nonetheless, all five estimates confirm that it is currently warmer than the late 19th century, i.e., there has been some “global warming” since the 19th century. For each of the five estimates of Northern Hemisphere temperatures, the contribution from direct solar forcing for all sixteen estimates of TSI was evaluated using simple linear least-squares fitting. The role of human activity on recent warming was then calculated by fitting the residuals to the UN IPCC’s recommended “anthropogenic forcings” time series. For all five Northern Hemisphere temperature series, different TSI estimates suggest everything from no role for the Sun in recent decades (implying that recent global warming is mostly human-caused) to most of the recent global warming being due to changes in solar activity (that is, that recent global warming is mostly natural). It appears that previous studies (including the most recent IPCC reports) which had prematurely concluded the former, had done so because they failed to adequately consider all the relevant estimates of TSI and/or to satisfactorily address the uncertainties still associated with Northern Hemisphere temperature trend estimates. Therefore, several recommendations on how the scientific community can more satisfactorily resolve these issues are provided.

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