Physics
Scientific paper
Jan 1987
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987jgr....92..823w&link_type=abstract
Journal of Geophysical Research, Volume 92, Issue D1, p. 823-827
Physics
5
Scientific paper
A program to measure the variability of solar spectrum lines in the visible wavelengths began in 1974 at Kitt Peak Observatory and continues as we approach the minimum between solar cycles 21 and 22. Both photospheric and chromospheric lines are measured on a monthly basis using an optical system that permits observation of the irradiance from the full solar disk as well as a smaller region near the center of the sun's disk. The full disk measurements of the Ca II K line quantify the increase and subsequent decrease in line flux with the change in solar activity. However, spectra of quiet regions at disk center show little if any variation throughout the cycle. Photospheric lines separate into two classes according to their variability: low-excitation lines of neutral metals resemble the K line in the shape of their solar cycle variability curve, but weaker lines formed deeper in the photosphere show no variation from 1974 to 1986. All of these findings point to solar activity as the source of the observed spectral variations, but the largest radiometric effects occur in chromospheric lines, with little or no evidence of variability in lines found deep in the photosphere.
Livingston William Charles
Wallace Laura
White Oran Richard
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