Measurements of the solar soft X‐ray irradiance from the Student Nitric Oxide Explorer

Beginning on March 11, 1998, the Student Nitric Oxide Explorer (SNOE) satellite has made daily observations of the solar soft x‐ray irradiance. These measurements are carried out by a multi‐channel photometer system utilizing x‐ray sensitive photodiodes with individual thin film filters. Current from the photodiodes is analyzed in terms of a solar reference spectrum in order to determine solar irradiances. The irradiances from 2 to 10 nm vary between 0.15 and 0.40 ergs cm−2 s−1 from March 11 to July 19, 1998 while the solar 10.7 cm fluxes varied between 85 and 140 × 10−22 W m−2 Hz−1. A 27‐day periodicity is observed with variations in the soft x‐ray irradiance on the order of a factor of two. The measured irradiances are shown to be correlated with the solar 10.7 cm flux but only mildly so with the GOES‐8 0.1 to 0.8 nm solar fluxes.