Title: Variations In Solar Euv Flux As Measured By SOHO/CELIAS/SEM

Authors: Pap, J. M., D. Judge, D. McMullin and L. Floyd

Reference: SOHO 11 Workshop, Davos, Switzerland (2002)

Solar EUV irradiance has been measured by the CELIAS/SEM on the SOHO experiment since January 1996, providing data from solar minimum to maximum conditions. These measurements cover two spectral ranges: the broader 0.1 50 nm (central order channel, often called as XUV) and in the 26 34 nm (first order channel, often called as EUV). To study the relation betwen the XUV and EUV irradiances, a ratio (Ratio = XUV/EUV) has been derived. This XUV/EUV ratio is compared to the 0.1 5 nmspectral range (so-called _ value) as calculated from the SEM measurements, representing the soft X-ray part of the SEM irradiance measurements. It is shown that the XUV/EUGV ratio and _ are closely related and both indices rise slowly over the solar cycle. The most interesting events in the derived ratio and _ are the sharp spikes which are associated with the increased sunspot areas derived from the SOHO/MDI images and the rapid increases in the GOES soft X-ray data. Results on the SEM irradiance variations and their interpretation are presented in this paper.

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Last Update: 25 March 2003, Xuyu Wang