Abstract
Measurement of the full disk Ca II H and K profiles has now been completed from minimum to maximum in the current solar cycle 21. The central intensity of the K line increases by 30% on the average, but a peak change of +40% was recorded near the maximum of solar activity in late 1979. The 1 A K index shows a corresponding but smaller increase of 18%. These changes in the Sun viewed as a star appear to be directly attributable to the occurrence of solar plages on the visible solar hemisphere. Similar measurements of a 1' x 3' quiet region at disk center show no significant systematic variability. This suggests that the quiet network has no long-term variability in the rising phase of the solar cycle. Ca II K line widths and asymmetries also show systematic changes associated with the degree of solar activity. In general, spectral features formed above the temperature minimum are all closely correlated in their variablitity, but they are not well related to changes in the strength of narrow photospheric lines and the K/sub 1/ wings. Ca II variability correlates very closely with the plage index, the Zurich sunspot number, and the Ottawa 10more » cm flux measurements. The observing program will continue into the declining phase of cycle 21, so we will have the opportunity to test the constancy of our correlations in a different phase of the cycle when the rate of sunspot formation is decreasing and when Ca II variability may be influenced more by the remnants of active regions formed earlier.« less
Published Version
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