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.