The discrepancy in solar EUV-proxy correlations on solar cycle and solar rotation timescales and its manifestation in the ionosphere

摘要

This study investigates the correlations between SOHO/Solar EUV Monitor 26-34 nm EUV and the F10.7 and Mg II proxies on solar cycle (long-term) and solar rotation (short-term) timescales. The long-term components of EUV and proxies are well correlated, and the general relation between them can be captured by the 81 day averaged EUV and proxies. Short-term EUV-proxy correlation is poorer and variable during the solar cycle. The slopes of short-term EUV against proxies vary from solar rotation to solar rotation, and they are generally lower than those of long-term EUV against proxies. EUV and proxies show discrepant evolutions during the episode of major active regions, which should be a primary reason for the poorer short-term EUV-proxy correlation and the variable short-term EUV-proxy slope. Mg II is a better proxy than F10.7 for 26-34 nm EUV. Its superiority mainly comes from better indications for short-term EUV. Global electron content (GEC) significantly responds to the long-term and short-term variations of EUV. Accordingly, the correlations between short-term GEC and proxies are poorer, and they are obviously lower than those between short-term EUV and proxies owing to ionospheric day-to-day variability. Short-term GEC-proxy slopes are also lower than the long-term slopes. F10.7 and Mg II are improved by combining the daily and 81 day averaged components of them with weighted factors that are designed to decrease the difference between long-term and short-term EUV-proxy slopes. The improved proxies can effectively upgrade the indications of proxies for EUV though they cannot solve the variability of short-term EUV-proxy slope. This method is also used to improve proxies for better indicating GEC, but the improved proxies for GEC differ from those for 26-34 nm EUV.