Full-disc Ca II K observations -- a window to past solar magnetism

Abstract

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.

arXiv comment47 pages, 13 figures, accepted for publication in Frontiers in Astronomy and Space Sciences

References in corpus (71)

• The Solar Orbiter mission -- Science overview
• Solar Irradiance Variability and Climate
• Sunrise: instrument, mission, data and first results
• The new Sunspot Number: assembling all corrections
• Reconstruction of the Sunspot Group Number: the Backbone Method
• The Magnetic Field in the Solar Atmosphere
• A Revised Collection of Sunspot Group Numbers
• Reconstruction of total and spectral solar irradiance from 1974 to 2013 based on KPVT, SoHO/MDI and SDO/HMI observations
• The second flight of the SUNRISE balloon-borne solar observatory: overview of instrument updates, the flight, the data and first results
• A New Calibrated Sunspot Group Series Since 1749: Statistics of Active Day Fractions
• Sun-as-a-Star Spectrum Variations 1974-2006
• Quiet Sun magnetic fields observed by Hinode: Support for a local dynamo
• New reconstruction of the sunspot group number since 1739 using the direct calibration and "backbone" methods
• Solar Irradiance Variability is Caused by the Magnetic Activity on the Solar Surface
• Sunspot area catalogue revisited: Daily cross-calibrated areas since 1874
• Relation between photospheric magnetic field and chromospheric emission
• Hemispheric sunspot numbers 1874--2020
• The Mount Wilson Ca II K index
• The relationship between chromospheric emissions and magnetic field strength
• Analysis of full disc Ca II K spectroheliograms. II. Towards an accurate assessment of long-term variations in plage areas
• Analysis of full disc Ca II K spectroheliograms III. Plage area composite series covering 1892-2019
• Latitudinal variation of the solar photospheric intensity
• Correlation Between Sunspot Number and ca II K Emission Index
• The Chromospheric Telescope
• Butterfly Diagram and Carrington Maps for Century-Long Ca II K Spectroheliograms from Kodaikanal Observatory
• Analysis of full disc Ca II K spectroheliograms. I. Photometric calibration and CLV compensation
• PICARD SODISM, a space telescope to study the Sun from the middle ultraviolet to the near infrared
• The Dimmest State of the Sun
• Recovering the unsigned photospheric magnetic field from Ca II K observations
• Brightness of Solar Magnetic Elements as a Function of Magnetic Flux at High Spatial Resolution
• Updated sunspot group number reconstruction for 1749-1996 using the active day fraction method
• Modelling a multi-spacecraft coronal mass ejection encounter with EUHFORIA
• Observing Evolution in the Supergranular Length Scale During Periods of Low Solar Activity
• Variation of Supergranule Parameters With Solar Cycles: Results From Century-Long Kodaikanal Digitized Ca II K Data
• Radiative emission of solar features in the Ca II K line: comparison of measurements and models
• Reconstructing solar irradiance from historical Ca II K observations. I. Method and its validation
• Solar-Cycle Characteristics in Kodaikanal Sunspot Area: North--South Asymmetry, Phase Distribution and Gnevyshev Gap
• Modelling solar irradiance from ground-based photometric observations
• Total Solar Irradiance during the Last Five Centuries
• The Intensity Profile of the Solar Supergranulation
• The Solar Ultraviolet Imaging Telescope onboard Aditya-L1
• A tilted interference filter in a converging beam
• Long term study of the solar filaments from the Synoptic Maps as derived from $H_{\alpha }$ Spectroheliograms of Kodaikanal Observatory
• How different are the Liège and Hamburg atlases of the solar spectrum?
• Delving into the Historical Ca II K Archive from the Kodaikanal Observatory: the Potential of the Most Recent Digitised Series
• Scrutinizing the relationship between plage areas and sunspot areas and numbers
• Kanzelhöhe Observatory: instruments, data processing and data products
• The New 2018 Version of the Meudon Spectroheliograph
• Long-Term Evolution of the Sun's magnetic field during Cycles 15--19 based on their proxies from Kodaikanal Solar Observatory
• On the variability of the solar mean magnetic field: contributions from various magnetic features on the surface of the Sun
• Long-term Variations in the Intensity of Plages and Networks as Observed in Kodaikanal Ca-K Digitized Data
• Association of Plages With Sunspots: A multi wavelength Study Using Kodaikanal Ca $\text{II}$ K and Greenwich sunspot area Data
• How faculae and network relate to sunspots, and the implications for solar and stellar brightness variations
• Characterization of chromospheric activity based on Sun-as-a-star spectral and disk-resolved activity indices
• Intensity contrast of solar plage as a function of magnetic flux at high spatial resolution
• Chromospheric Synoptic Maps of Polar Crown Filaments
• Determining the Variations of Ca-K index and Features using a Century Long Equal Contrast Images from Kodaikanal Observatory
• Image Quality Assessment for Full-Disk Solar Observations with Generative Adversarial Networks
• The cyclic behaviour in the N-S asymmetry of sunspots and solar plages for the period 1910 to 1937 using data from Ebro catalogues
• Association Of Supergranule Mean Scales with Solar Cycle Strengths and Total Solar Irradiance
• Variation of Chromospheric Features as a Function of Latitude and Time using Ca-K Spectroheliograms for Solar Cycles 15-23: Implications for Meridional Flow
• Signature of Extended Solar Cycles as Detected from Ca II K Synoptic Maps of Kodaikanal and Mount Wilson Observatory
• Reconstructing solar magnetic fields from historical observations VIII. AIA 1600 Å contrast as a proxy of solar magnetic fields
• The solar survey at Pic du Midi: calibrated data and improved images
• Network and Plage Indices from Kodaikanal Ca-K Data
• Solar supergranular fractal dimension dependence on the Solar cycle phase
• Solar Hα excess during Solar Cycle 24 from full-disk filtergrams of the Chromospheric Telescope
• A Full-disk Image Standardization of the Chromosphere Observation at Huairou Solar Observing Station
• Determination of the chromospheric quiet network element area index and its variation during 2008-2011
• Ca II K 1-A Emission Index Composites
• Twin Telescope observations of the Sun at Kodaikanal Observatory

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• Re-calibration of the Sunspot Number: Status Report
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• Analysis of full-disc H alpha observations: Carrington maps and filament properties in 1909-2022
• Investigating the effect of solar ambient and data characteristics on Ca II K observations and line profile measurements
• Solar photospheric spectrum microvariability II. Observed relations to magnetic activity and radial-velocity modulation
• Revisiting the SATIRE-S irradiance reconstruction: Heritage of Mt Wilson magnetograms and Ca II K observations
• Variations of the Ca II K Line Profile Parameters with Solar Latitude and Time Observed from Kodaikanal Solar Observatory
• Solar Irradiance Reconstruction over the Telescopic Era Using a Revised Photospheric Magnetic Field Model
• Reconstruction of total solar irradiance variability as simultaneously apparent from Solar Orbiter and Solar Dynamics Observatory