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Title: POLAR NETWORK INDEX AS A MAGNETIC PROXY FOR THE SOLAR CYCLE STUDIES

The Sun has a polar magnetic field which oscillates with the 11 yr sunspot cycle. This polar magnetic field is an important component of the dynamo process which operates in the solar convection zone and produces the sunspot cycle. We have direct systematic measurements of the Sun's polar magnetic field only from about the mid-1970s. There are, however, indirect proxies which give us information about this field at earlier times. The Ca-K spectroheliograms taken at the Kodaikanal Solar Observatory during 1904-2007 have now been digitized with 4k × 4k CCD and have higher resolution (∼0.86 arcsec) than the other available historical data sets. From these Ca-K spectroheliograms, we have developed a completely new proxy (polar network index, hereafter PNI) for the Sun's polar magnetic field. We calculate PNI from the digitized images using an automated algorithm and calibrate our measured PNI against the polar field as measured by the Wilcox Solar Observatory for the period 1976-1990. This calibration allows us to estimate the polar fields for the earlier period up to 1904. The dynamo calculations performed with this proxy as input data reproduce reasonably well the Sun's magnetic behavior for the past century.
Authors:
; ; ;  [1] ;  [2] ;  [3] ;  [4]
  1. Indian Institute of Astrophysics,Koramangala, Bengaluru 560034 (India)
  2. Nordita, KTH Royal Institute of Technology and Stockholm University (Sweden)
  3. Montana State University, Bozeman, MT 59717 (United States)
  4. Indian Institute of Science, Bangalore (India)
Publication Date:
OSTI Identifier:
22365035
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 793; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ALGORITHMS; CALIBRATION; CHARGE-COUPLED DEVICES; CONVECTION; FACULAE; INDEXES; MAGNETIC FIELDS; PLAGES; RESOLUTION; SOLAR CYCLE; SUN; SUNSPOTS