Solar Variability from the Mg II and Ca II Indices

M. Snow, J. Harder, W. McClintock, E. Richard, and T. Woods

Space based spectrometers have observed the Sun as a star on a daily basis in the ultraviolet for over 30 years. The record of the Mg II core-to-wing ratio is an important proxy for solar variability, and solar EUV variability in particular. The Mg II h & k lines at 280 nm cannot be observed from the ground. However, a chemically similar ion, Ca II, has lines in the visible part of the spectrum (H & K) near 395 nm. The Ca II K index from full-disk integrated observations has an even longer data record. In this project, we compare the variability observed via these two solar indices, with particular attention paid to the recent observations from the SOlar Radiation and Climate Experiment (SORCE).

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