An empirical model of the variation of the solar Lyman-α spectral irradiance

Abstract : We propose a simple model that computes the spectral profile of the solar irradiance in the hydrogen Lyman alpha line, H Ly-α(121.567nm), from 1947 to present. Such a model is relevant for the study of many astronomical environments, from planetary atmospheres to interplanetary medium. This empirical model is based on the SOHO/SUMER observations of the Ly-α irradiance over Solar Cycle 23 and the Ly-α disk-integrated irradiance composite. The model reproduces the temporal variability of the spectral profile and matches the independent SORCE/SOLSTICE spectral observations from 2003 to 2007 with an accuracy better than 10%.