THE SOLAR CA-II-K INDEX AND THE MG-II CORE-TO-WING RATIO

The 1angstrom index of the solar Ca II K line is compared with the core-to-wing ratio of satellite measurements of the Mg II h and k lines. The correlation coefficient r = 0.976 for the Nimbus-7 Mg II ratio during solar cycle 21 and r = 0.99 for the NOAA9 Mg II ratio in cycle 22. Linear regression analysis for the full dynamic range of both data sets is used to combine the Nimbus-7 and NOAA9 Mg II data. These relations permit the ground-based Ca K index to estimate the solar UV flux.