A 10-Year Set of Ca II K-Line Filtergrams

We have processed a 10-year set of BBSO Caii K-line filtergrams covering most of solar cycle 22. The excess K-line emission is integrated to form linear and square-root activity indices that are fitted to UV data from UARS and SME. Good fits are found both for the Mgii core–wing ratio (linear) and total L irradiance (square root) and the indices are thus good proxies for UV data. The SME L irradiance is systematically lower by 20% than predicted from our corresponding K-line indices. The 10.7 cm radio data confirms that SME underestimated the flux. The network is partly responsible for the solar cycle variation of the indices and is relatively more important in L than in Mgii and Caii K. This is due to the saturation of L equivalent width. We also report on substantial improvements to the equipment and reduction software. The system is now based on a digital CCD camera which promises more accurate measurements in the upcoming solar cycle 23.