An evaluation of the correlation between open solar flux and total solar irradiance

Abstract

The correlation between the coronal source flux F_S and the total solar irradiance I_TS is re-evaluated in the light of an additional 5 years' data from the rising phase of solar cycle 23 and also by using cosmic ray fluxes detected at Earth. Tests on monthly averages show that the correlation with F_S deduced from the interplanetary magnetic field (correlation coefficient, r = 0.62) is highly significant (99.999%), but that there is insufficient data for the higher correlation with annual means (r = 0.80) to be considered significant. Anti-correlations between I_TS and cosmic ray fluxes are found in monthly data for all stations and geomagnetic rigidity cut-offs (r ranging from -0.63 to -0.74) and these have significance levels between 85% and 98%. In all cases, the fit is poorest for the earliest data (i.e., prior to 1982). Excluding these data improves the anticorrelation with cosmic rays to r = -0.93 for one-year running means. Both the interplanetary magnetic field data and the cosmic ray fluxes indicate that the total solar irradiance lags behind the open solar flux with a delay that is estimated to have an optimum value of 2.8 months (and is within the uncertainty range 0.8-8.0 months at the 90% level).