Reconstructing solar irradiance from Ca II K observations

Chatzistergos, Theodosios; Krivova, N. A.; Ermolli, I.; Yeo, Kok Leng; Solanki, S. K.; Puiu, Cosmin C.; Giorgi, F.; Mandal, Sudip

doi:10.1002/essoar.10505862.1

Cited by 8 publications

(14 citation statements)

References 34 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…We note that over SC 23 the plage areas in all backbone series except the RP1 exhibit a secondary peak around 2004. This is attributed to the Ko data over that period as was also mentioned by Chatzistergos et al (2019c).…”

Section: Plage Areas Compositesupporting

confidence: 61%

“…In this study, we present a plage area composite obtained on the basis of the results from 38 datasets. These include the data from the 16-bit digitisation of the Ko dataset (Chatzistergos et al 2019c) as well as the recently recovered data from the 16-bit digitisation of MW. Furthermore, we use a different methodology to create our plage area composite series, employing the "backbone" approach (Svalgaard & Schatten 2016;Chatzistergos et al 2017).…”

Section: Plage Areas Compositementioning

confidence: 99%

See 1 more Smart Citation

Analysis of full disc Ca II K spectroheliograms III. Plage area composite series covering 1892-2019

Chatzistergos,

Ermolli,

Krivova

et al. 2020

Preprint

Self Cite

View full text Add to dashboard Cite

Context. Studies of long-term solar activity and variability require knowledge of the past evolution of the solar surface magnetism. An important source of such information are the archives of full-disc Ca II K observations performed more or less regularly at various sites since 1892. Aims. We derive the plage area evolution over the last 12 solar cycles employing data from all Ca II K archives available publicly in digital form known to us, including several as yet unexplored Ca II K archives. Methods. We analyse more than 290,000 full-disc Ca II K observations from 43 datasets spanning the period 1892-2019. All images were consistently processed with an automatic procedure that performs the photometric calibration (if needed) and the limb-darkening compensation. The processing also accounts for artefacts plaguing many of the images, including some very specific artefacts such as bright arcs found in Kyoto and Yerkes data. The employed methods have previously been tested and evaluated on synthetic data and found to be more accurate than other methods used in the literature to treat a subset of the data analysed here. Results. We have produced a plage area time-series from each analysed dataset. We found that the differences between the plage areas derived from individual archives are mainly due to the differences in the central wavelength and the bandpass used to acquire the data at the various sites. We have empirically cross-calibrated and combined the results obtained from each dataset to produce a composite series of plage areas. "Backbone" series are used to bridge all the series together. We have also shown that the selection of the backbone series has little effect on the final plage area composite. We have quantified the uncertainty of determining the plage areas with our processing due to shifts in the central wavelength and found it to be less than 0.01 in fraction of the solar disc for the average conditions found on historical data. We also found the variable seeing conditions during the observations to slightly increase the plage areas during activity maxima. Conclusions. We provide the so far most complete time series of plage areas based on corrected and calibrated historical and modern Ca II K images. Consistent plage areas are now available on 88% of all days from 1892 onwards and on 98% from 1907 onwards.

show abstract

Section: Plage Areas Compositesupporting

confidence: 61%

Section: Plage Areas Compositementioning

confidence: 99%

Analysis of full disc Ca II K spectroheliograms III. Plage area composite series covering 1892-2019

Chatzistergos,

Ermolli,

Krivova

et al. 2020

Preprint

Self Cite

View full text Add to dashboard Cite

show abstract

“…It has already been shown earlier (Wenzler et al 2009;Krivova et al 2009a;Yeo et al 2014;Chatzistergos et al 2021) that the choice of the TSI reference record does not significantly affect the value of the free parameter, B sat , and thus the final reconstructions. Here, we nevertheless tested this again.…”

Section: Results For Rp Observationsmentioning

confidence: 86%

“…The value of B sat affects mainly the amplitude of the cycle variation, with higher values of B sat returning weaker cycle amplitudes. The long-term trend is, however, barely affected by the selection of B sat within the range of values derived with the various reference series (see also Chatzistergos et al 2021). The correlation coefficient, R, is ∼0.9 or higher, while the RMS stays below 0.25 Wm −2 in all cases.…”

Section: Results For Rp Observationsmentioning

confidence: 93%

Reconstructing solar irradiance from historical Ca II K observations

Chatzistergos

Krivova

Ermolli

et al. 2021

A&A

Self Cite

View full text Add to dashboard Cite

Context. Knowledge of solar irradiance variability is critical to Earth’s climate models and understanding the solar influence on Earth’s climate. Direct solar irradiance measurements have only been available since 1978. Reconstructions of past variability typically rely on sunspot data. However, sunspot records provide only indirect information on the facular and network regions, which are decisive contributors to irradiance variability on timescales of the solar cycle and longer. Aims. Our ultimate goal is to reconstruct past solar irradiance variations using historical full-disc Ca II K observations to describe the facular contribution independently of sunspot observations. Here, we develop the method and test it extensively by using modern CCD-based (charge-coupled device) Ca II K observations. We also carry out initial tests on two photographic archives. Methods. We employ carefully reduced and calibrated Ca II K images from 13 datasets, including some of the most prominent series, such as those from the Meudon, Mt Wilson, and Rome observatories. We convert them to unsigned magnetic field maps and then use them as input to the adapted Spectral and Total Irradiance Reconstruction (SATIRE) model to reconstruct total solar irradiance (TSI) variations over the period 1978–2019, for which direct irradiance measurements are available. Results. The reconstructed irradiance from the analysed Ca II K archives agrees well with direct irradiance measurements and existing reconstructions. The model also returns good results on data taken with different bandpasses and images with low spatial resolution. Historical Ca II K archives suffer from numerous inconsistencies, but we show that these archives can still be used to reconstruct TSI with reasonable accuracy provided the observations are accurately processed and the effects of changes in instrumentation and instrumental parameters are identified and accounted for. The reconstructions are relatively insensitive to the TSI reference record used to fix the single free parameter of the model. Furthermore, even employment of a series, itself reconstructed from Ca II K data, as a reference for further reconstructions returns nearly equally accurate results. This will enable the Ca II K archives without an overlap with direct irradiance measurements to be used to reconstruct past irradiance. Conclusions. By using the unsigned magnetic maps of the Sun reconstructed from modern high-quality Ca II K observations as input into the SATIRE model, we can reconstruct solar irradiance variations nearly as accurately as from directly recorded magnetograms. Historical Ca II K observations can also be used for past irradiance reconstructions but need additional care, for example identifying and accounting for discontinuities and changes in the quality of the data with time.

show abstract

“…Until now, most studies used CCD-based Ca II K data for irradiance reconstructions, covering shorter periods than the direct TSI measurements (Chapman et al, 1996;Chapman et al, 2013;Ermolli et al, 2003b;Ermolli et al, 2011;Penza et al, 2003;Walton et al, 2003;Fontenla and Landi, 2018;Puiu, 2019;Chatzistergos et al, 2020a;Choudhary et al, 2020). Notwithstanding the short interval, such data allowed an assessment of the accuracy of the irradiance reconstructions.…”

Section: Irradiance Reconstructionmentioning

confidence: 99%

Full-disc Ca ii K observations—A window to past solar magnetism

Chatzistergos

Krivova

Ermolli

2022

Front. Astron. Space Sci.

View full text Add to dashboard Cite

Full-disc observations of the Sun in the Ca ii K line provide one of the longest collections of solar data. First such observations were made in 1892 and since then various sites around the world have carried out regular observations, with Kodaikanal, Meudon, Mt Wilson, and Coimbra being some of the most prominent ones. By now, Ca ii K observations from over 40 different sites allow an almost complete daily coverage of the last century. Ca ii K images provide direct information on plage and network regions on the Sun and, through their connection to solar surface magnetic field, offer an excellent opportunity to study solar magnetism over more than a century. This makes them also extremely important, among others, for solar irradiance reconstructions and studies of the solar influence on Earth’s climate. However, these data also suffer from numerous issues, which for a long time have hampered their analysis. Without properly addressing these issues, Ca ii K data cannot be used to their full potential. Here, we first provide an overview of the currently known Ca ii K data archives and sources of the inhomogeneities in the data, before discussing existing processing techniques, followed by a recap of the main results derived with such data so far.

show abstract

Reconstructing solar irradiance from Ca II K observations

Cited by 8 publications

References 34 publications

Analysis of full disc Ca II K spectroheliograms III. Plage area composite series covering 1892-2019

Analysis of full disc Ca II K spectroheliograms III. Plage area composite series covering 1892-2019

Reconstructing solar irradiance from historical Ca II K observations

Full-disc Ca ii K observations—A window to past solar magnetism

Contact Info

Product

Resources

About