130 years of spectroheliograms at Paris-Meudon observatories (1893–2023)

Malherbe, Jean-Marie

doi:10.1177/00218286231184193

Journal for the History of Astronomy

2023

DOI: 10.1177/00218286231184193

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130 years of spectroheliograms at Paris-Meudon observatories (1893–2023)

Jean-Marie Malherbe

Abstract: Broad-band observations of the solar photosphere began in Meudon in 1875 under the auspices of Jules Janssen. For his part, Henri Deslandres initiated imaging spectroscopy in 1892 at Paris observatory. He invented, concurrently with George Hale in Kenwood (USA), but quite independently, the spectroheliograph designed for monochromatic imagery of the solar atmosphere. Deslandres developed two kinds of spectrographs: the ‘ spectrohéliographe des formes’, that is, the narrow bandpass instrument to reveal chromosp… Show more

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Cited by 8 publications

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Butterfly Diagram and Other Properties of Plage Areas from Kodaikanal Ca ii K Photographs Covering 1904 – 2007

Jha,

Chatzistergos,

Banerjee

et al. 2024

Sol Phys

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Ca ii K observations of the Sun have a great potential for probing the Sun’s magnetism and activity, as well as for reconstructing solar irradiance. The Kodaikanal Solar Observatory (KoSO) in India, houses one of the most prominent Ca ii K archives, spanning from 1904 to 2007, obtained under the same experimental conditions over a century, a feat very few other sites have achieved. However, the KoSO Ca ii K archive suffers from several inconsistencies (e.g., missing/incorrect timestamps of observations and orientation of some images) which have limited the use of the archive. This study is a step towards bringing the KoSO archive to its full potential. We did this by developing an automatic method to orient the images more accurately than in previous studies. Furthermore, we included more data than in earlier studies (considering images that could not previously be analyzed by other techniques, as well as 2845 newly digitized images), while also accounting for mistakes in the observational date/time. These images were accurately processed to identify plage regions along with their locations, enabling us to construct the butterfly diagram of plage areas from the entire KoSO Ca ii K archive covering 1904 – 2007. Our butterfly diagram shows significantly fewer data gaps compared to earlier versions due to the larger set of data used in this study. Moreover, our butterfly diagram is consistent with Spörer’s law for sunspots, validating our automatic image orientation method. Additionally, we found that the mean latitude of plage areas calculated over the entire period is $20.5\%\pm 2.0$ 20.5 % ± 2.0 higher than that of sunspots, irrespective of the phase or the strength of the solar cycle. We also studied the north–south asymmetry showing that the northern hemisphere dominated plage areas during solar cycles 19 and 20, while the southern hemisphere dominated during Solar Cycles 21 – 23.

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Butterfly Diagram and Other Properties of Plage Areas from Kodaikanal Ca ii K Photographs Covering 1904 – 2007

Jha,

Chatzistergos,

Banerjee

et al. 2024

Sol Phys

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

Chatzistergos,

Ermolli,

Banerjee

et al. 2023

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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.

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Understanding the secular variability of solar irradiance: the potential of Ca II K observations

Chatzistergos,

Krivova,

Ermolli

2024

J. Space Weather Space Clim.

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With the increasing concern about climate change it is important to have accurate information on the individual contributions by the potential driving agents, solar variability being one of them. Long and reliable records of solar irradiance, which describes the solar radiative energy input into the climate system, are essential for assessing the role of the Sun. The short temporal extent (since the 1970s) of direct space-based irradiance measurements leaves reconstructions of the past variability with the help of models as the only avenue. Such models require information on the surface distribution and evolution of solar magnetic regions, dark sunspots and bright faculae and network. However, such data become increasingly scarce and of diminishing quality further back in time. Prior to the period of direct irradiance measurements, reconstructions mainly rely on sunspot observations or other indirect data to describe facular and network regions. The resulting estimates of the long-term change between the Maunder minimum and the present diverge by about an order of magnitude. Having direct information on bright magnetic regions can help resolving these discrepancies. The by far most promising data for this purpose are the full-disc observations of the Sun in the Ca II K line. Despite the wealth of such data all the way back to 1892, their use up to now has been rather limited, owing to a number of intricacies of the data. Here we review the recent efforts to bring Ca II K datasets to their full potential. We briefly discuss the problems plaguing the data and processing methods that have been developed to account for them before switching to a summary of the products derived from them. Focus is given on reconstructions of total and spectral irradiance variations from Ca II K observations. We summarise most available such reconstructions and discuss various aspects requiring further attention in order to allow Ca II K observations to be used to their full potential and thus eventually more accurate irradiance reconstructions back to 1892.

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130 years of spectroheliograms at Paris-Meudon observatories (1893–2023)

Cited by 8 publications

References 25 publications

Butterfly Diagram and Other Properties of Plage Areas from Kodaikanal Ca ii K Photographs Covering 1904 – 2007

Butterfly Diagram and Other Properties of Plage Areas from Kodaikanal Ca ii K Photographs Covering 1904 – 2007

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

Understanding the secular variability of solar irradiance: the potential of Ca II K observations

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