Correlation Between Sunspot Number and ca II K Emission Index

Abstract

Long-term synoptic observations in the resonance line of Ca II K constitute a fundamental database for a variety of retrospective analyses of the state of the solar magnetism. Synoptic Ca II K observations began in late 1904 at the Kodaikanal Observatory, in India. In early 1970s, the National Solar Observatory (NSO) at Sacramento Peak (USA) started a new program of daily Sun-as-a-star observations in the Ca II K line. Today the NSO is continuing these observations through its Synoptic Optical Long-term Investigations of the Sun (SOLIS) facility. These different data sets can be combined into a single disk-integrated Ca II K index time series that describes the average properties of the chromospheric emission over several solar cycles. We present such a Ca II K composite and discuss its correlation with the new entirely revised sunspot number data series. For this preliminary investigation, the scaling factor between pairs of time series was determined assuming a simple linear model for the relationship between the monthly mean values during the duration of overlapping observations.

arXiv comment16 pages, 8 figures, accepted for publication in Solar Physics

References in corpus (7)

• Solar Irradiance Variability and Climate
• The Mount Wilson Ca II K index
• The relationship between chromospheric emissions and magnetic field strength
• Improvements in the determination of ISS Ca II K parameters
• Solar physics at the Kodaikanal Observatory: A Historical Perspective
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• Updating the Historical Sunspot Record

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