The variable Sun is the most likely candidate for natural forcing of past climate change on time scales of 50 to 1000 years. Evidence for this understanding is that the terrestrial climate correlates positively with solar activity. During the past 10,000 years, the Sun has experienced substantial variations in activity and there have been numerous attempts to reconstruct solar irradiance. While there is general agreement on how solar forcing varied during the last several hundred years --- all reconstructions are proportional to the solar activity --- there is scientific controversy on the magnitude of solar forcing. We present a reconstruction of the Total and Spectral Solar Irradiance covering 130 nm--10 $μ$m from 1610 to the present with annual resolution and for the Holocene with 22-year resolution. We assume that the minimum state of the quiet Sun in time corresponds to the observed quietest area on the present Sun. Then we use available long-term proxies of the solar activity, which are $^{10}$Be isotope concentrations in ice cores and 22-year smoothed neutron monitor data, to interpolate between the present quiet Sun and the minimum state of the quiet Sun. This determines the long-term trend in the solar variability which is then superposed with the 11-year activity cycle calculated from the sunspot number. The time-dependent solar spectral irradiance from about 7000 BC to the present is then derived using a state-of-the-art radiation code. We derive a total and spectral solar irradiance that was substantially lower during the Maunder minimum than observed today. The difference is remarkably larger than other estimations published in the recent literature. The magnitude of the solar UV variability, which indirectly affects climate is also found to exceed previous estimates. We discuss in details the assumptions which leaded us to this conclusion.
Context. There is no consensus on the amplitude of the historical solar forcing. The estimated magnitude of the total solar irradiance difference between Maunder minimum and present time ranges from 0.1 to 6 W/m2 making uncertain the simulation of the past and future climate. One reason for this disagreement is the applied evolution of the quiet Sun brightness in the 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 of the…
We address the importance of historical full disc Ca II K spectroheliograms for solar activity and irradiance reconstruction studies. We review our work on processing such data to enable them to be used in irradiance reconstructions. We also present our preliminary estimates of the plage areas from five of the longest available historical Ca II K archives.
In this paper, we demonstrate the importance of embedding temporal information for an accurate prediction of solar irradiance. We have used two sets of models for forecasting solar irradiance. The first one uses only time series data of solar irradiance for predicting future values. The second one uses the historical solar irradiance values, together with the corresponding timestamps. We employ data from the weather station located at Nanyang Technological University (NTU) Singapore. The solar irradiance values are recorded with a temporal resolution of $1$ minute, for a period of $1$ year. We…
The reconstruction and prediction of solar activity is one of the current problems in dynamo theory and global climate modeling. We estimate the Total Solar Irradiance for the next hundred years based on the Least Square Support Vector Machine. We found that the next secular solar minimum will occur between the years 2003 and 2063 with an average of 1365.4W/m2 close to the Dalton or Modern minima. We calculate the radiative forcing between the modern maximum and the 21st century minimum to be -0.1W/m2.
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 are only available since 1978. Reconstructions of past variability typically rely on sunspot data. These 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. Our ultimate goal is to reconstruct past solar irradiance variations using historical full-disc Ca II K observations to describe the facular contri…
The Sun's net radiative output varies on timescales of minutes to gigayears. Direct measurements of the total solar irradiance (TSI) show changes in the spatially- and spectrally-integrated radiant energy on timescales as short as minutes to as long as a solar cycle. Variations of ~0.01 % over a few minutes are caused by the ever-present superposition of convection and oscillations with very large solar flares on rare occasion causing slightly-larger measureable signals. On timescales of days to weeks, changing photospheric magnetic activity affects solar brightness at the ~0.1 % level. The 11…
The total solar irradiance (TSI) varies on timescales of minute to centuries. On short timescales it varies due to the superposition of intensity fluctuations produced by turbulent convection and acoustic oscillations. On longer scale times, it changes due to photospheric magnetic activity, mainly because of the facular brightenings and dimmings caused by sunspots. While modern TSI variations have been monitored from space since 1970s, TSI variations over much longer periods can only be estimated using either historical observations of magnetic features, possibly supported by flux transport mo…
We analyze the long-term behavior of supergranule scale parameter, in active and quiet regions (AR, QR), using the Kodaikanal digitized data archive. This database provides century-long daily full disc observations of the Sun in Ca-II K wavelength. In this paper, we study the distributions of the supergranular scales, over the whole data duration, which show identical shape in these two regimes. We found that the AR mean scale values are always higher than that of the QR for every solar cycle. The mean scale values are highly correlated with the sunspot number cycle amplitude and also with tot…
One of the objectives of the NASA LWS Institute on Nowcasting of Atmospheric Drag for LEO Spacecraft was to investigate whether and how to increase the accuracy of atmospheric drag models by improving the quality of the solar forcing inputs, namely Extreme Ultraviolet (EUV) irradiance information. In this focused review, we examine the status of and issues with EUV measurements and proxies, discuss recent promising developments, and suggest a number of ways to improve the reliability, availability, and forecast accuracy of EUV measurements in the next solar cycle.
Recently published, precise stellar photometry of 72 Sun-like stars obtained at the Fairborn Observatory between 1993 and 2017 is used to set limits on the solar forcing of Earth's atmosphere of $\pm$ 4.5 W m$^{-2}$ since 1750. This compares with the +2.2 $\pm$ 1.1 W m$^{-2}$ IPCC estimate for anthropogenic forcing. Three critical assumptions are made. In decreasing order of importance they are: (a) most of the brightness variations occur within the average time-series length of $\approx$17 years; (b) the Sun seen from the ecliptic behaves as an ensemble of middle-aged solar-like stars; and (c…
Reliable historical records of total solar irradiance (TSI) are needed for climate change attribution and research to assess the extent to which long-term variations in the Sun's radiant energy incident on the Earth may exacerbate (or mitigate) the more dominant warming in recent centuries due to increasing concentrations of greenhouse gases. We investigate potential impacts of the new Sunspot Index and Long-term Solar Observations (SILSO) sunspot-number time series on model reconstructions of TSI. In contemporary TSI records, variations on time scales longer than about a day are dominated by …
Total solar irradiance variations, about 0.1% between solar activity maximum and minimum, are available from accurate satellite measurements since 1978 and thus do not provide useful information on longer-term secular trends. Recently, Krivova et al., 2007 reconstructed, using suitable models, the total solar irradiance from the end of the Maunder minimum to the present, based on variations of the surface distribution of the solar magnetic field. The latter is calculated from the long historical record of the sunspot numbers using a simple but consistent physical model. There are many classes …
The variation of solar irradiance is one of the natural forcing mechanisms of the terrestrial climate. Hence, the time-dependent solar irradiance is an important input parameter for climate modelling. The solar surface magnetic field is a powerful proxy for solar irradiance reconstruction. The analyses of data obtained with the Michelson Doppler Imager (MDI) on board the SOHO mission are therefore useful for the identification of solar surface magnetic features to be used in solar irradiance reconstruction models. However, there is still a need for automated technologies that would enable the …
Many observational records critically rely on our ability to merge different (and not necessarily overlapping) observations into a single composite. We provide a novel and fully-traceable approach for doing so, which relies on a multi-scale maximum likelihood estimator. This approach overcomes the problem of data gaps in a natural way and uses data-driven estimates of the uncertainties. We apply it to the total solar irradiance (TSI) composite, which is currently being revised and is critical to our understanding of solar radiative forcing. While the final composite is pending decisions on wha…
Context: The study of variations in total solar irradiance (TSI) is important for understanding how the Sun affects the Earth's climate. Aims: Full-disk continuum images and magnetograms are now available for three full solar cycles. We investigate how modelled TSI compares with direct observations by building a consistent modelled TSI dataset. The model, based only on changes in the photospheric magnetic flux can then be tested on rotational, cyclical and secular timescales. Methods: We use Kitt Peak and SoHO/MDI continuum images and magnetograms in the SATIRE-S model to reconstruct TSI over …
This paper contributes to the field of modeling and hindcasting of the total solar irradiance (TSI) based on different proxy data that extend further back in time than the TSI that is measured from satellites. We introduce a simple method to analyze persistent frequency-dependent correlations (FDCs) between the time series and use these correlations to hindcast missing historical TSI values. We try to avoid arbitrary choices of the free parameters of the model by computing them using an optimization procedure. The method can be regarded as a general tool for pairs of data sets, where correlati…
The historical record of sunspot areas is a valuable and widely used proxy of solar activity and variability. The Royal Greenwich Observatory (RGO) regularly measured this and other parameters between 1874 and 1976. After that time records from a number of different observatories are available. These, however, show systematic differences and often have significants gaps. Our goal is to obtain a uniform and complete sunspot area time series by combining different data sets. A homogeneus composite of sunspot areas is essential for different applications in solar physics, among others for irradia…
Empirical evidences show that planetary tides may influence solar activity: 1) the 11-yr Schwabe sunspot number cycle is constrained between the spring tidal period of Jupiter and Saturn, 9.93 yr, and the tidal orbital period of Jupiter, 11.86 yr, and a model based on these cycles reconstructs solar dynamics at multiple time ; 2) a measure of the alignment of Venus, Earth and Jupiter reveals quasi 11.07-yr cycles well correlated to the 11-year Schwabe solar cycles; 3) there exists a 11.08 yr cyclical recurrence in the solar jerk-shock vector, which is induced mostly by Mercury and Venus. Howev…
Context. Monitoring of the photometric and chromospheric HK emission data series of stars similar to the Sun in age and average activity level showed that there is an empirical correlation between the average stellar chromospheric activity level and the photometric variability. In general, more active stars show larger photometric variability. Interestingly, the measurements and reconstructions of the solar irradiance show that the Sun is significantly less variable than indicated by the empirical relationship. Aims. We aim to identify possible reasons for the Sun to be currently outside of th…
The satellite total solar irradiance (TSI) database provides a valuable record for investigating models of solar variation used to interpret climate changes. The 35-year ACRIM TSI satellite composite was updated using corrections to ACRIMSAT/ACRIM3 results derived from recent testing at the Laboratory for Atmospheric and Space Physics/Total solar irradiance Radiometer Facility (LASP/TRF). The corrections lower the ACRIM3 scale by ~5000 ppm, in close agreement with the scale of SORCE/TIM results (solar constant ~1361 W/m^2). Relative variations and trends are not changed. Differences between th…
The time series of total solar irradiance (TSI) satellite observations since 1978 provided by ACRIM and PMOD TSI composites are studied. We find empirical evidence for planetary-induced forcing and modulation of solar activity. Power spectra and direct data pattern analysis reveal a clear signature of the 1.09-year Earth-Jupiter conjunction cycle, in particular during solar cycle 23 maximum. This appears to suggest that the Jupiter side of the Sun is slightly brighter during solar maxima. The effect is observed when the Earth crosses the Sun-Jupiter conjunction line every 1.09 years. Multiple …
Luminosity, which is the total amount of radiant energy emitted by an object, is one of the most critical quantities in astrophysics for characterizing stars. Equally important is the temporal evolution of a star's luminosity because of its intimate connection with the stellar energy budget, large-scale convective motion, and heat storage in the stellar interior. Here, we model the solar luminosity by extending a semi-empirical total solar irradiance (TSI) model that uses solar-surface magnetism to reconstruct solar irradiance over the entire 4π solid angle around the Sun. This model was const…
Historical Reconstruction of Solar Surface Magnetism from Cycle 1-24 Using the Synthetic Active Region Generator (SARG) and the Advective Flux Transport (AFT) Model
Reconstructions of total solar irradiance (TSI) rely mainly on linear relations between TSI variation and indices of facular area. When these are extrapolated to the prolonged 15th - 17th century Spörer and Maunder solar activity minima, the estimated solar dimming is insufficient to explain the mid- millennial climate cooling of the Little Ice Age. We draw attention here to evidence that the relation departs from linearity at the lowest activity levels. Imaging photometry and radiometry indicate an increased TSI contribution per unit area from small network faculae by a factor of 2-4 compared…
The historical Hungarian auroral record extends from 1523 to 1960 and is longer than the sunspot record. Harmonic analysis reveals four major multidecadal secular cycles forming an approximate harmonic set at periods of 42.85, 57.13, 85.7 and 171.4 years. These four frequencies are very close to the four major heliospheric oscillations relative to the center of mass of the solar system caused by Jupiter, Saturn, Uranus and Neptune. Similar frequencies are found in solar radiation models based on long cosmogenic isotope records (Steinhilber et al. 2012) and in long records of naked-eye sunspot …
Reconstructions of past irradiance variations require suitable data on solar activity. The longest direct proxy is the sunspot number, and it has been most widely employed for this purpose. These data, however, only provide information on the surface magnetic field emerging in sunspots, while a suitable proxy of the evolution of the bright magnetic features, specifically faculae/plage and network, is missing. This information can potentially be extracted from the historical full-disc observations in the Ca II K line. We have analysed over 100,000 historical images from 8 digitised photographic…
How the solar electromagnetic energy entering the Earth's atmosphere varied since pre-industrial times is an important consideration in the climate change debate. Detrimental to this debate, estimates of the change in total solar irradiance (TSI) since the Maunder minimum, an extended period of weak solar activity preceding the industrial revolution, differ markedly, ranging from a drop of 0.75 Wm-2 to a rise of 6.3 Wm-2. Consequently, the exact contribution by solar forcing to the rise in global temperatures over the past centuries remains inconclusive. Adopting a novel approach based on stat…
Records of observations of sunspots and auroras in pre-telescopic historical documents provide useful information about past solar activity both in long-term trends and short-term space weather events. In this study, we present the results of a comprehensive survey of the records of sunspots and aurora candidates in the Yuánshǐ and Míngshǐ, Chinese Official Histories spanning 1261-1368 and 1368-1644, based on continuous observations with well-formatted reportds conducted by contemporary professional astronomers. We then provide a brief comparison of these data with Total Solar Irradiance (TSI)…
Solar flares strongly affect the Sun's atmosphere as well as the Earth's environment. Quantifying the maximum possible energy of solar flares of the present-day Sun, if any, is thus a key question in heliophysics. The largest solar flares observed over the past few decades have reached energies of a few times 10^{32} ergs, possibly up to 10^{33} ergs. Flares in active Sun-like stars reach up to about 10^{36} ergs. In the absence of direct observations of solar flares within this range, complementary methods of investigation are needed. Using historical reports for solar active region, we scale…
