Reconstruction Of Solar Irradiance Research Articles

Analysis of full-disc Hαobservations: Carrington maps and filament properties in 1909–2022

Context.Full-disc observations of the Sun in the Hαline provide information about the solar chromosphere, and in particular, about the filaments, which are dark and elongated features that lie along magnetic field polarity-inversion lines. This makes them important for studies of solar magnetism. Because full-disc Hαobservations have been performed at various sites since the second half of the 19th century, with regular photographic data having started at the beginning of the 20th century, they are an invaluable source of information on past solar magnetism.Aims.We derive accurate information about filaments from historical and modern full-disc Hαobservations.Methods.We consistently processed observations from 15 Hαarchives spanning 1909–2022. The analysed datasets include long-running ones such as those from Meudon and Kodaikanal, but also previously unexplored datasets such as those from Arcetri, Boulder, Larissa, and Upice. Our data processing includes photometric calibration of the data stored on photographic plates, the compensation for limb-darkening, and the orientation of the data to align solar north at the top of the images. We also constructed Carrington maps from the calibrated Hαimages.Results.We find that filament areas, similar to plage areas in Ca IIK data, are affected by the bandwidth of the observation. Thus, a cross calibration of the filament areas derived from different archives is needed. We produced a composite of filament areas from individual archives by scaling all of them to the Meudon series. Our composite butterfly diagram very distinctly shows the common features of filament evolution, that is, the poleward migration as well as a decrease in the mean latitude of filaments as the cycle progresses. We also find that during activity maxima, filaments cover ∼1% of the solar surface on average. The change in the amplitude of cycles in filament areas is weaker than in sunspot and plage areas.Conclusions.Analysis of Hαdata for archives with contemporaneous Ca IIK observations allowed us to identify and verify archive inconsistencies, which also have implications for reconstructions of past solar magnetism and irradiance from Ca IIK data.

Millennial-Scale Solar Variability in Tree Rings of Northern Fennoscandia at the End of the Holocene

To investigate the possible Sun–climate connection during the Holocene, the Finnish super-long tree-ring chronology covering the period from 5634 B.C. to A.D. 2004 was analyzed. As an indicator of solar activity, we used a reconstruction of total solar irradiance (TSI) covering 9300 years, which is based on a composite using the cosmogenic radionuclide 10Be measured in polar ice cores, and also on neutron monitor data (Steinhilber et al. 2009). The Multiple Taper Method (MTM) wavelet decomposition and wavelet coherence analyses were applied to the time-series. The MTM spectral analysis identifies the main solar cycles at ca. 200 yr (de Vries or Suess), ca. 350 yr (unnamed) and ca. 900 years (Eddy). The strongest cross-wavelet correlation was discovered between the millennium-cycle components of TSI and tree-ring width variations. This Eddy cycle, which was recently discovered in solar activity, remains both strong and stable through almost the entire Holocene, and it reappears again at lower frequencies (ca. 1300 years) after ca. A.D. 200. Our results raise questions regarding the end of the Holocene and transition to the next glacial period and confirm the complex and nonlinear nature of the Sun–climate relationship during the Holocene Epoch.

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

Full-disc observations of the Sun in the Ca iiK 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 iiK observations from over 40 different sites allow an almost complete daily coverage of the last century. Ca iiK 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 iiK data cannot be used to their full potential. Here, we first provide an overview of the currently known Ca iiK 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.

Scrutinising the relationship between plage areas and sunspot areas and numbers

Context. Studies and reconstructions of past solar activity require data on all magnetic regions on the surface of the Sun (i.e. on dark sunspots as well as bright faculae–plage and network). Such data are also important for understanding the magnetic activity and variability of the Sun and Sun-like stars. The longest available direct faculae–plage datasets are white-light facular and Ca II K observations going back to 1874 and 1892, respectively. Prior to that time the only direct data available are for sunspots. Aims. We reassess the relationship between plage areas and sunspot records (areas and numbers) since 1892, to allow reconstructions of facular–plage areas which can be employed for studies going further back in time to the period when solely sunspot observations are available. Methods. We use the plage areas derived from 38 consistently processed Ca II K archives as well as the plage area composite based on these archives. The considered archives include both the well-known observatories (e.g. Coimbra, Kodaikanal, Meudon, Mt Wilson), and the less explored observatories (e.g. Kharkiv, Mees, and Upice). These data allow us to study the relationship between plage area and sunspot records (areas and number) over a period of 12 solar cycles and for different bandpasses. Results. We find the relationship between plage and sunspot areas to be well represented by a power-law function; the relationship between the plage areas and the sunspot number is also best fit with a power-law function. We further find that the relationships depend on the bandwidth and the solar cycle strength. The reconstructions with a power-law relationship are in good agreement with the original plage area series, whereas employment of a cycle-strength-dependent relationship improves the reconstructions only marginally. We also estimate the error in the plage areas reconstructed from the sunspot areas or numbers. Performing the same analysis on other previously published plage area series, usually derived from a single archive with diverse processing techniques, returns different results when using different time series. This highlights the importance of applying a consistent processing to the various archives and demonstrates the uncertainties introduced by using previously published series for studies of past solar activity, including irradiance reconstructions. Conclusions. Our results have implications for past solar activity and irradiance reconstructions and for stellar activity studies, which sometimes assume a linear dependence between plage and sunspot areas.

Investigation of the Long-term Variation of Solar Ca ii K Intensity. II. Reconstruction of Solar UV Irradiance

Abstract Reconstruction of long-term solar UV variations during the entire 20th century is reported. The sunspot number has been used for this purpose so far. By using the full-disk Ca K intensity as an additional solar UV proxy, the range of allowed values for the reconstructed UV irradiance becomes more restricted. We use long-term archival data of the photographic Ca K plates digitized at the Kodaikanal Solar Observatory. The photographic calibration method developed in our previous paper (Paper I) is applied. Various long-term proxy data of solar activity have been used to estimate past UV irradiance. In light of this context, some issues using the historical Ca K data are commented on.

A Reconstruction of Total Solar Irradiance Based on Wavelet Analysis

AbstractAs an important indicator of solar activity, the long‐term total solar irradiance (TSI) observations are needed to uncover the impact of solar activity on Earth's climate. In this paper, the periodic variation of TSI and its relationships with sunspot number and Ca II K index are analyzed by using the satellite observation data from 1979 to 2015 and the wavelet method. The results of continuous wavelet analysis show that TSI, sunspot number and Ca II K index all have significant and stable oscillation periods of 9∼13 years and intermittent oscillation periods of 2∼6 months only during the time of intense solar activity. Moreover, the results of cross wavelet analysis indicate that the effect of sunspot number and Ca II K index on TSI is mainly reflected in the period of 9∼13 years with one month phase lag, and sunspot number and Ca II K index cannot explain the TSI variation in the period of 3∼6 months. Under the condition of considering the phase relationship and the model order, the TSI reconstruction model is established and the monthly TSI time series from 1907 to 1978 is restored.

A reconstruction of total solar irradiance based on wavelet analysis

A reconstruction of total solar irradiance based on wavelet analysis

Scaling Properties and Persistence of Long-Term Solar Activity

The long-range correlations associated with the presence of persistence are investigated by applying the detrended fluctuation analysis (DFA) on three different proxies of long-term solar activity. The considered datasets are a sunspot number reconstruction (SNR04) obtained from the atmospheric activity of the cosmogenic isotope 14C derived from tree rings, a total solar irradiance reconstruction (TSIR12) obtained from several 10Be ice core records from Greenland and Antarctica in combination with the global record of 14C in tree rings and a new multi-proxy sunspot number reconstruction (SNR18), also derived from 10Be datasets and the global 14C production series. The DFA scaling exponents found for the three time series are similar (lying in the range between 0.70 and 0.77) and the scaling ranges are comparable. These results indicate the presence of long-range correlations with persistence, in substantial agreement with the findings of previous studies carried out on other solar activity indices and proxies.

Reconstruction of Total Solar Irradiance by Deep Learning

The Earth's primary source of energy is the radiant energy generated by the Sun, which is referred to as solar irradiance, or total solar irradiance (TSI) when all of the radiation is measured. A minor change in the solar irradiance can have a significant impact on the Earth's climate and atmosphere. As a result, studying and measuring solar irradiance is crucial in understanding climate changes and solar variability. Several methods have been developed to reconstruct total solar irradiance for long and short periods of time; however, they are physics-based and rely on the availability of data, which does not go beyond 9,000 years. In this paper we propose a new method, called TSInet, to reconstruct total solar irradiance by deep learning for short and long periods of time that span beyond the physical models' data availability. On the data that are available, our method agrees well with the state-of-the-art physics-based reconstruction models. To our knowledge, this is the first time that deep learning has been used to reconstruct total solar irradiance for more than 9,000 years.

Solar Activity Predictability Horizons

The chaotic component in solar-activity variations, the limited amount of observational statistics, and the use of proxy data impose limitations on long-term predictions. This study uses the well-known reconstructions of total solar irradiance (TSI) from optical observations (from 1610 AD) and cosmogenic radioisotopes (from 7362 BC) to estimate the maximum Lyapunov exponent for 11-year and secular cycles. This is done with the classical algorithm described by Wolf et al. (1985). The maximum Lyapunov exponents turned out to be positive in both cases, thus confirming the presence of the chaotic component in time series. We then estimate the predictability horizon Tp with the well-known error for each reconstruction. It turned out that the predictability horizon is on average 10 ≤ Tp ≤ 22 years for 11-year cycles and on average 40 ≤ Tp ≤ 60 years for secular cycles.

Forecasting long-term solar activity with time series models: Some cautionary findings

Long-term forecasting of solar activity, over a scale of centuries, is of interest in modeling climate. Reconstructions of solar irradiance based on radionuclides span 9.4 to 11.5 millennia. There is evidence of multiple maxima and minima, as well as changes in trend. Analysis of the data yields ambiguous results. Fourier spectra find long cycles in the data, but these are not confirmed in the time domain. The autocorrelation function decays slowly over a period of several decades, indicating that the data is probably not predictable beyond these horizons. Wavelet analysis indicates that the energy is spread out over a range of frequencies, making it impossible to identify cycles at fixed periodicities. This paper tests time series and artificial intelligence models. Forecasting experiments are run over horizons ranging from 44 to 250 years. At 44 years the models do reasonably well, but beyond about 88 years, the models do not forecast effectively. The deterioration in accuracy is observed in all the methods tested. Despite the finding of low-frequency peaks in the spectrum, models incorporating long cycles do particularly badly. The failure of the models to predict at longer horizons supports the interpretation that the sun has chaotic or stochastic properties. The forecasts are consistent with simulation studies in which maxima and minima occur at irregular intervals, making their timing unpredictable.

Sunspot area catalog revisited: Daily cross-calibrated areas since 1874

Context. Long and consistent sunspot area records are important for understanding long-term solar activity and variability. Multiple observatories around the globe have regularly recorded sunspot areas, but such individual records only cover restricted periods of time. Furthermore, there are systematic differences between these records and require cross-calibration before they can reliably be used for further studies. Aims. We produce a cross-calibrated and homogeneous record of total daily sunspot areas, both projected and corrected, covering the period between 1874 and 2019. In addition, we generated a catalog of calibrated individual group areas for the same period. Methods. We compared the data from nine archives: Royal Greenwich Observatory (RGO), Kislovodsk, Pulkovo, Debrecen, Kodaikanal, Solar Optical Observing Network (SOON), Rome, Catania, and Yunnan Observatories, covering the period between 1874 and 2019. Cross-comparisons of the individual records were done to produce homogeneous and inter-calibrated records of daily projected and corrected areas. As in earlier studies, the basis of the composite is formed by the data from RGO. After 1976, the only datasets used are those from Kislovodsk, Pulkovo, and Debrecen observatories. This choice was made based on the temporal coverage and the quality of the data. While there are still 776 days missing in the final composite, these remaining gaps could not be filled with data from the other archives as the missing days lie either before 1922 or after 2016 and none of the additional archives cover these periods. Results. In contrast to the SOON data used in previous area composites for the post-RGO period, the properties of the data from Kislovodsk and Pulkovo are very similar to those from the RGO series. They also directly overlap the RGO data in time, which makes their cross-calibration with RGO much more reliable. Indeed, comparing our area catalog with previous such composites, we find improvements both in data quality and coverage. We also computed the daily Photometric Sunspot Index, which is widely used, for example, in empirical reconstructions of solar irradiance.

Placing limits on long-term variations in quiet-Sun irradiance and their contribution to total solar irradiance and solar radiative forcing of climate

Recent reconstructions of total solar irradiance (TSI) postulate that quiet-Sun variations could give significant changes to the solar power input to Earth's climate (radiative climate forcings of 0.7-1.1 W m-2 over 1700-2019) arising from changes in quiet-Sun magnetic fields that have not, as yet, been observed. Reconstructions without such changes yield solar forcings that are smaller by a factor of more than 10. We study the quiet-Sun TSI since 1995 for three reasons: (i) this interval shows rapid decay in average solar activity following the grand solar maximum in 1985 (such that activity in 2019 was broadly equivalent to that in 1900); (ii) there is improved consensus between TSI observations; and (iii) it contains the first modelling of TSI that is independent of the observations. Our analysis shows that the most likely upward drift in quiet-Sun radiative forcing since 1700 is between +0.07 and -0.13 W m-2. Hence, we cannot yet discriminate between the quiet-Sun TSI being enhanced or reduced during the Maunder and Dalton sunspot minima, although there is a growing consensus from the combinations of models and observations that it was slightly enhanced. We present reconstructions that add quiet-Sun TSI and its uncertainty to models that reconstruct the effects of sunspots and faculae.

Comparing Radiative Transfer Codes and Opacity Samplings for Solar Irradiance Reconstructions

Some techniques developed to reproduce solar irradiance variations make use of synthetic radiative fluxes of quiet and magnetic features. The synthesis of radiative fluxes of astronomical objects is likely to be affected by uncertainties resulting from approximations and specific input employed for the synthesis. In this work we compare spectra obtained with three radiative transfer codes with the purpose of investigating differences in reproducing solar irradiance variations. Specifically, we compare spectral synthesis produced in non-local thermodynamic equilibrium obtained with COSI and RH using 1-D atmosphere models. We also compare local thermodynamic equilibrium syntheses emerging from 3-D MURaM simulations of the solar atmosphere obtained with two sets of opacity tables generated with the ATLAS9 package and with the RH code, and test the effects of opacity sampling on the emergent spectra. We find that, although the different codes and methodologies employed to synthesize the spectrum reproduce overall the observed solar spectrum with a similar degree of accuracy, subtle differences in quiet Sun spectra may translate into larger differences in the computation of the contrasts of magnetic features, which, in turn, critically affect the estimates of solar variability.

RETRACTED ARTICLE: Oscillations of the baseline of solar magnetic field and solarirradiance on a millennial timescale

Recently discovered long-term oscillations of the solar backgroundmagnetic field associated with double dynamo waves generated in inner and outerlayers of the Sun indicate that the solar activity is heading in the next threedecades (2019–2055) to a Modern grand minimum similar to Maunder one. On the otherhand, a reconstruction of solar total irradiance suggests that since the Maunderminimum there is an increase in the cycle-averaged total solar irradiance (TSI) by avalue of about 1–1.5 Wm−2 closely correlated with an increaseof the baseline (average) terrestrial temperature. In order to understand these twoopposite trends, we calculated the double dynamo summary curve of magnetic fieldvariations backward one hundred thousand years allowing us to confirm strongoscillations of solar activity in regular (11 year) and recently reported grand(350–400 year) solar cycles caused by actions of the double solar dynamo. Inaddition, oscillations of the baseline (zero-line) of magnetic field with a periodof 1950 ± 95 years (a super-grand cycle) are discovered by applying a runningaveraging filter to suppress large-scale oscillations of 11 year cycles. Latestminimum of the baseline oscillations is found to coincide with the grand solarminimum (the Maunder minimum) occurred before the current super-grand cycle start.Since then the baseline magnitude became slowly increasing towards its maximum at2600 to be followed by its decrease and minimum at ~3700. These oscillations of thebaseline solar magnetic field are found associated with a long-term solar inertialmotion about the barycenter of the solar system and closely linked to an increase ofsolar irradiance and terrestrial temperature in the past two centuries. This trendis anticipated to continue in the next six centuries that can lead to a furthernatural increase of the terrestrial temperature by more than 2.5 °C by 2600.

Solar total and spectral irradiance reconstruction over the last 9000 years

Context.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.Aims.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.Methods.The concentrations of the cosmogenic isotopes14C and10Be 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.Results.We present the first ever SSI reconstruction over the last 9000 years from the individual14C and10Be 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.Conclusions.Irradiance reconstructions based on two different cosmogenic isotope records, those of14C and10Be, 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−2. 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 lowerχ2-value.

Late Holocene hydroclimatic variations and possible forcing mechanisms over the eastern Central Asia

Hydroclimatic variations over the eastern Central Asia are highly sensitive to changes in hemispheric-scale atmospheric circulation systems. To fully understand the long-term variability and relationship between hydroclimate and atmospheric circulation system, we present a high-resolution lascustrine record of late Holocene hydroclimate from Lake Sayram, Central Tianshan Mountains, China, based on the total organic carbon, total nitrogen, and carbonate contents, carbon/nitrogen ratios, and grain size. Our results reveal four periods of substantially increased precipitation at the interval of 4000–3780, 3590–3210, 2800–2160, and 890–280 cal yr BP, and one period of slightly increased precipitation from 1700–1370 cal yr BP. These wetter periods broadly coincide with those identified in other records from the mid-latitude Westerlies-dominated eastern Central Asia, including the northern Tibetan Plateau. As such, a similar hydroclimatic pattern existed over this entire region during the late Holocene. Based on a close similarity of our record with reconstruction of North Atlantic Oscillation indices and solar irradiance, we propose that decreased solar irradiance and southern migration of the entire circum-North Atlantic circulation system, particularly the main pathway of the mid-latitude Westerlies, significantly influenced hydroclimate in eastern Central Asia during the late Holocene. Finally, the inferred precipitation at Lake Sayram has increased markedly over the past 100 years, although this potential future changes in hydroclimate in Central Asia need for further investigation.

Recent progresses in the use of 3D MHD simulations for solar irradiance reconstructions

AbstractThe use of 3D magneto-hydrodynamic simulations of the solar atmosphere in modeling irradiance variations seems a natural evolution of the current irradiance reconstruction techniques making use of one-dimensional, static, atmosphere models. Nevertheless, the development of such new models poses serious computational challenges. This contribution focuses on recent progresses made in the development of novel irradiance reconstruction models making use of 3D MHD simulations and discusses current and future challenges.

Revised historical solar irradiance forcing

Context. There is no consensus on the amplitude of historical solar forcing. The estimated magnitude of the total solar irradiance (TSI) difference between the Maunder minimum and the present time ranges from 0.1 to 6 W m−2 making the simulation of the past and future climate uncertain. One reason for this disagreement is the applied evolution of the quiet Sun brightness in solar irradiance reconstruction models. This work addresses the role of the quiet Sun model choice and updated solar magnetic activity proxies on the solar forcing reconstruction. Aims. We aim to establish a plausible range for the solar irradiance variability on decadal to millennial timescales. Methods. The spectral solar irradiance (SSI) is calculated as a weighted sum of the contributions from sunspot umbra, sunspot penumbra, faculae, and quiet Sun, which are pre-calculated with the NLTE Spectral SYnthesis code (NESSY). We introduce activity belts of the contributions from sunspots and faculae and a new structure model for the quietest state of the Sun. We assume that the brightness of the quiet Sun varies in time proportionally to the secular (22-yr smoothed) variation of the solar modulation potential. Results. A new reconstruction of the TSI and SSI covering the period 6000 BCE - 2015 CE is presented. The model simulates solar irradiance variability during the satellite era well. The TSI change between the Maunder and recent minima ranges between 3.7 and 4.5 W m−2 depending on the applied solar modulation potential. The implementation of a new quietest Sun model reduces, by approximately a factor of two, the relative solar forcing compared to the largest previous estimation, while the application of an updated solar modulation potential increases the forcing difference between the Maunder minimum and the present by 25–40%.

A new method for reconstruction of solar irradiance

The purpose of this research is to show how time series should be reconstructed using an example with the data on total solar irradiation (TSI) of the Earth and on sunspot numbers (SSN) since 1749. The traditional approach through regression equation(s) is designed for time-invariant vectors of random variables and is not applicable to time series, which present random functions of time. The autoregressive reconstruction (ARR) method suggested here requires fitting a multivariate stochastic difference equation to the target/proxy time series. The reconstruction is done through the scalar equation for the target time series with the white noise term excluded. The time series approach is shown to provide a better reconstruction of TSI than the correlation/regression method. A reconstruction criterion is introduced which allows one to define in advance the achievable level of success in the reconstruction. The conclusion is that time series, including the total solar irradiance, cannot be reconstructed properly if the data are not treated as sample records of random processes and analyzed in both time and frequency domains.