Correlation Between Sunspot Number and Ca ii K Emission Index

• Published in: Solar physics Vol. 291; no. 9-10; pp. 2967 - 2979
• Main Authors: Bertello, Luca, Pevtsov, Alexei, Tlatov, Andrey, Singh, Jagdev
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01-11-2016; Springer Nature B.V
• Subjects: Astrophysics and Astroparticles; Atmospheric Sciences; Correlation; Emission; K lines; Magnetic fields; Magnetism; Physics; Physics and Astronomy; Solar cycle; Solar observatories; Solar physics; Space Exploration and Astronautics; Space Sciences (including Extraterrestrial Physics; Sunspot Number Recalibration; Sunspots; Time series; USA; USA, California, Sacramento; India; Magnetic fields, Chromosphere; Chromosphere, Active; Solar Irradiance
• ISSN: 0038-0938; 1573-093X
• DOI: 10.1007/s11207-016-0927-9

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 the 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.