Estimation of solar EUV flux from TIMED/GUVI data

Abstract

This paper examines the relationships between the integrated solar EUV (26–34 nm and 5–45 nm) flux and the measured radiance in the N2 Lyman-Birge-Hopfield (LBH) 140–150 nm range (LBHS) under sunlit conditions. We find that both the (26–34 nm) and (5–45 nm) solar fluxes are linearly correlated with the daily median LBHS radiances with correlation coefficients of 0.979 and 0.963 respectively. Such a linear correlation can provide an alternative way to estimate the integrated solar EUV flux, a key heating and ionization source for the thermosphere and ionosphere. A direct measurement of the solar EUV spectrum is challenging due to a rapid degradation of EUV instruments. We demonstrate that using an FUV instrument to infer the change in the solar EUV flux, to the accuracy needed for aeronomic applications, leads to a more stable estimation of the solar EUV inputs especially over the long time scales that are important for understanding secular changes in the upper atmosphere.