Magnetic and radiative variability of solar surface structures. I. Image decomposition and magnetic-intensity mapping

In order to specify quantitatively the contributions to irradiance variability by specific types of solar surface structure, we analyzed full-disk magnetograms and Ca II K images from the National Solar Observatory and Big Bear Solar Observatory for two sets of several days in early 1992 and mid-1993. These test days were chosen at maxima and minima of the rotational modulation in the Ly alpha irradiance from the Upper Atmosphere Research Satellite Solar-Stellar Irradiance Comparison Experiment (UARS/SOLSTICE) spectrometer. For the eight days, we isolated active regions, decaying active regions, the enhanced network, the network, and the quiet atmosphere based on their magnetic flux strength and distribution, filling factor, and association with sunspots. Transfer of these image decompositions to Ca II K images gives magnetic flux versus intensity (\B\ vs. delta K) relationships for four structures with measurable magnetic flux. In the range 30-400 Mx cm(-2), these log-log curves are linear with a slope of 0.5, which suggests that the Ca II K residual intensity is proportional to the half-power of the magnetic flux density. The separation into quiet and active Sun structures gives a prediction of the variation of the \B\ versus delta K relation for the ensemble of our four principal structures from minimum to maximum in the activity cycle of the Sun viewed as a star.