A 10-year set of Ca II K-line filtergrams

We have processed a 10-year set of BBSO Ca II 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 Mg II core-wing ratio (linear) and total L alpha irradiance (square root) and the indices are thus good proxies for UV data. The SME L alpha 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 Bur. The network is partly responsible for the solar cycle variation of the indices and is relatively more important in La than in Mg II and Ca II K. This is due to the saturation of L alpha 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.