A Century of Solar Ca ii Measurements and Their Implication for Solar UV Driving of Climate

Foukal, P.; Bertello, L.; Livingston, W.; Pevtsov, Alexei A.; Singh, Jagdev; Tlatov, A. G.; Ulrich, R. K.

doi:10.1007/s11207-009-9330-0

Cited by 71 publications

(53 citation statements)

References 21 publications

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“…For F10.7, there is also no significant change back to the start of the measurements in1947. The CaII K index deduced from the Mt Wilson observations (Foukal et al 2009b) back to around 1915 shows also no change in the minima to within ±4%. As the chromospheric indices are highly correlated with the UV and EUV irradiance, secular changes of the spectral irradiance below about 300 nm are hence unlikely.…”

Section: Correlation With the Open Solar Magnetic Fieldmentioning

confidence: 83%

Evidence of a long-term trend in total solar irradiance

Fröhlich¹

2009

A&A

202

200

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Aims. During the solar minimum of 2008, the value of total solar irradiance at 1 AU (TSI) was more than 0.2 Wm −2 lower than during the last minimum in 1996, indicating for the first time a directly observed long-term change. On the other hand, chromospheric indices and hence solar UV irradiance do not exhibit a similar change. Methods. Comparison of TSI with other activity parameters indicates that only the open solar magnetic field, B R , observed from satellites at 1 AU show a similar long-term behaviour. The values at the minima correlate well and the linear fit provides a direct physical relationship between TSI and B R during the minimum times.Results. This correlation allows an unambiguous reconstruction of TSI back in time, provided the open solar magnetic field can be determined from e.g. geomagnetic indices or cosmogenic radionucleides. Since the solar UV irradiance has no long-term trend, the mechanism for the secular change of TSI must differ from the effect of surface magnetism, as manifested by sunspots, faculae, and network which indeed explain well the intra-cycle variability of both total and spectral irradiance. Conclusions. The long-term trend of TSI is most probably caused by a global temperature change of the Sun that does not influence the UV irradiance in the same way as the surface magnetic fields.

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Section: Correlation With the Open Solar Magnetic Fieldmentioning

confidence: 83%

Evidence of a long-term trend in total solar irradiance

Fröhlich¹

2009

A&A

202

200

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“…Note that the Ca K index has a pronounced non-linear variation with sunspot numbers (e.g. Foukal et al, 2009). …”

Section: The Mount Wilson Ca K Index [Caki]mentioning

confidence: 99%

Tests of Sunspot Number Sequences: 4. Discontinuities Around 1946 in Various Sunspot Number and Sunspot-Group-Number Reconstructions

2016

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We use five test data series to search for, and quantify, putative discontinuities around 1946 in five different annual-mean sunspot-number or sunspot-groupnumber data sequences. . These test data all vary in close association with sunspot numbers, in some cases non-linearly. The tests are carried out using both the before-and-after fitresidual comparison method and the correlation method of Lockwood, Owens, and Barnard, applied to annual mean data for intervals iterated to minimise errors and to eliminate uncertainties associated with the precise date of the putative discontinuity. It is not assumed that the correction required is by a constant factor, nor even linear in sunspot number. It is shown that a non-linear correction is required by R C , R BB , and R ISNv1 , but not by R ISNv2 or R UEA . The five test datasets give very similar results in all cases. By multiplying the probability distribution functions together, we obtain the optimum correction for each sunspot dataset that must be applied to pre-discontinuity data to make them consistent with the postdiscontinuity data. It is shown that, on average, values for 1932 -1943 and 5.2 %, respectively. The correction that was applied to generate R C from R ISNv1 reduces this average factor to 0.5 % but does not remove the non-linear variation with the test data, and other errors remain uncorrected. A valuable test of the procedures used is provided by R UEA , which is identical to the RGO N G values over the interval employed.

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“…Stenflo used Hinode SOT/SP deep mode data set in combination with constraints from the Hanle effect technique to argue that "there is evidence that the very substantial amount of magnetic energy that exists on small scales (below a few km) is physically related to and fed from the magnetic energy at large scales, which is generated by the global dynamo". Foukal (2012) has pointed out that the reconstructions of S2011 can be pitted against the photographic record of observations of the chromospheric network in Ca II K line data (Foukal et al 2009) available since 1907. The small changes in network structure may not be consistent with the 4 Wm −2 change in irradiance predicted by S2011 (Foukal & Milano 2001).…”

Section: Quiet Sun Magnetic Fields: Influenced By Global Magnetic Fiementioning

confidence: 99%

Confronting a solar irradiance reconstruction with solar and stellar data

Judge

Lockwood

Radick

et al. 2012

A&A

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Context. A recent paper by Shapiro and colleagues (2011, A&A, 529, A67) reconstructs spectral and total irradiance variations of the Sun during the holocene. Aims. In this note, we comment on why their methodology leads to large (0.5%) variations in the solar TSI on century-long time scales, in stark contrast to other reconstructions which have < ∼ 0.1% variations. Methods. We examine the amplitude of the irradiance variations from the point of view of both solar and stellar data. Results. Shapiro et al.'s large amplitudes arise from differences between the irradiances computed from models A and C of Fontenla and colleagues, and from their explicit assumption that the radiances of the quiet Sun vary with the cosmic ray modulation potential. We suggest that the upper photosphere, as given by model A, is too cool, and discuss relative contributions of local vs. global dynamos to the magnetism and irradiance of the quiet Sun. We compare the slow (>22 yr) components of the irradiance reconstructions with secular changes in stellar photometric data that span 20 years or less, and find that the Sun, if varying with such large amplitudes, would still lie within the distribution of stellar photometric variations measured over a 10−20 year period. However, the stellar time series are individually too short to see if the reconstructed variations will remain consistent with stellar variations when observed for several decades more. Conclusions. By adopting model A, Shapiro et al. have over-estimated quiet-Sun irradiance variations by about a factor of two, based upon a re-analysis of sub-mm data from the James Clerk Maxwell telescope. But both estimates are within bounds set by current stellar data. It is therefore vital to continue accurate photometry of solar-like stars for at least another decade, to reveal secular and cyclic variations on multi-decadal time scales of direct interest to the Sun.

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A Century of Solar Ca ii Measurements and Their Implication for Solar UV Driving of Climate

Cited by 71 publications

References 21 publications

Evidence of a long-term trend in total solar irradiance

Evidence of a long-term trend in total solar irradiance

Tests of Sunspot Number Sequences: 4. Discontinuities Around 1946 in Various Sunspot Number and Sunspot-Group-Number Reconstructions

Confronting a solar irradiance reconstruction with solar and stellar data

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