Solar EUV flux during sunspot cycles 21, 22 and 23—Correlation with proxy indices and real time prediction

Abstract

Langmuir probe on the Pioneer Venus Orbiter measured the total solar EUV flux during large portions of sunspot cycles 21 and 22, while CELIAS/Solar EUV Monitor (SEM) on the Solar and Heliospheric Observatory (SOHO) measured this flux in the spectral ranges 26-34 nm and 0.1-50 nm during the whole of sunspot cycle 23.In this paper, daily values of these EUV fluxes are studied in relation to various often-used proxy indices to identify a single index which has the highest correlation coefficient with the observed values during all the three sunspot cycles. It is observed that no single index exhibits this feature. However, almost all the proxy indices averaged over one-half or more solar rotations show a high degree of correlation with the daily EUV flux. Further, the solar magnetic field is found to exhibit somewhat better correlation and it is recommended that this index averaged over three previous solar rotations may be used for real time prediction of solar EUV flux.