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Solar total and spectral irradiance reconstruction over the last 9000 years
Wu, C.-J.,Krivova, N. A.,Solanki, S. K.,Usoskin, I. G. Springer-Verlag 2018 Astronomy and astrophysics Vol.620 No.-
<P><I>Context.</I> Changes in solar irradiance and in its spectral distribution are among the main natural drivers of the climate on Earth. However, irradiance measurements are only available for less than four decades, while assessment of solar influence on Earth requires much longer records.</P><P><I>Aims.</I> The aim of this work is to provide the most up-to-date physics-based reconstruction of the solar total and spectral irradiance (TSI/SSI) over the last nine millennia.</P><P><I>Methods.</I> The concentrations of the cosmogenic isotopes <SUP>14</SUP>C and <SUP>10</SUP>Be in natural archives have been converted to decadally averaged sunspot numbers through a chain of physics-based models. TSI and SSI are reconstructed with an updated SATIRE model. Reconstructions are carried out for each isotope record separately, as well as for their composite.</P><P><I>Results.</I> We present the first ever SSI reconstruction over the last 9000 years from the individual <SUP>14</SUP>C and <SUP>10</SUP>Be records as well as from their newest composite. The reconstruction employs physics-based models to describe the involved processes at each step of the procedure.</P><P><I>Conclusions.</I> Irradiance reconstructions based on two different cosmogenic isotope records, those of <SUP>14</SUP>C and <SUP>10</SUP>Be, agree well with each other in their long-term trends despite their different geochemical paths in the atmosphere of Earth. Over the last 9000 years, the reconstructed secular variability in TSI is of the order of 0.11%, or 1.5 W m<SUP>−2</SUP>. After the Maunder minimum, the reconstruction from the cosmogenic isotopes is consistent with that from the direct sunspot number observation. Furthermore, over the nineteenth century, the agreement of irradiance reconstructions using isotope records with the reconstruction from the sunspot number by Chatzistergos et al. (2017, A&A, 602, A69) is better than that with the reconstruction from the WDC-SILSO series (Clette et al. 2014, Space Sci. Rev., 186, 35), with a lower <I>χ</I><SUP>2</SUP>-value.</P>
Solar Cycle Variation in Solar Irradiance
Yeo, K. L.,Krivova, N. A.,Solanki, S. K. Springer Science + Business Media 2014 Space science reviews Vol.186 No.1
<P>The correlation between solar irradiance and the 11-year solar activity cycle is evident in the body of measurements made from space, which extend over the past four decades. Models relating variation in solar irradiance to photospheric magnetism have made significant progress in explaining most of the apparent trends in these observations. There are, however, persistent discrepancies between different measurements and models in terms of the absolute radiometry, secular variation and the spectral dependence of the solar cycle variability. We present an overview of solar irradiance measurements and models, and discuss the key challenges in reconciling the divergence between the two.</P>
Yeo, K. L.,Krivova, N. A.,Solanki, S. K.,Glassmeier, K. H. EDP Sciences 2014 Astronomy and astrophysics Vol.570 No.-
<P>Context. Total and spectral solar irradiance are key parameters in the assessment of solar influence on changes in the Earth’s climate. Aims. We present a reconstruction of daily solar irradiance obtained using the SATIRE-S model spanning 1974 to 2013 based on full-disc observations from the KPVT, SoHO/MDI, and SDO/HMI. Methods. SATIRE-S ascribes variation in solar irradiance on timescales greater than a day to photospheric magnetism. The solar spectrum is reconstructed from the apparent surface coverage of bright magnetic features and sunspots in the daily data using the modelled intensity spectra of these magnetic structures. We cross-calibrated the various data sets, harmonizing the model input so as to yield a single consistent time series as the output. Results. The model replicates 92% (R,<SUP>2</SUP> = 0.916) of the variability in the PMODTSI composite including the secular decline between the 1996 and 2008 solar cycle minima. The model also reproduces most of the variability in observed Lyman-α irradiance and the MgII index. The ultraviolet solar irradiance measurements from the UARS and SORCE missions are mutually consistent up to about 180 nm before they start to exhibit discrepant rotational and cyclical variability, indicative of unresolved instrumental effects. As a result, the agreement between model and measurement, while relatively good below 180 nm, starts to deteriorate above this wavelength. As with earlier similar investigations, the reconstruction cannot reproduce the overall trends in SORCE/SIM SSI. We argue, from the lack of clear solar cycle modulation in the SIM record and the inconsistency between the total flux recorded by the instrument and TSI, that unaccounted instrumental trends are present. Conclusions. The daily solar irradiance time series is consistent with observations from multiple sources, demonstrating its validity and utility for climate models. It also provides further evidence that photospheric magnetism is the prime driver of variation in solar irradiance on timescales greater than a day.</P>