Photoelectrons as a tool to evaluate spectral variations in solar EUV irradiance over solar cycle timescales

The largest differences between observed and modeled fluxes are in the 4-10 nm range, where the Fast Auroral Snapshot data show that the SEE Version 9 irradiances are systematically low. Our analysis suggests that variation on solar cycle timescales in the TIMED/SEE Version 9 and Flare Irradiance Spectral Model irradiance derived from them are systematically low in the 18-27 nm region. Because of uncertainties in the absolute value of the observed photoelectron fluxes and solar irradiances, differences between observed and modeled photoelectron fluxes are not sufficient to determine more exactly the magnitude of variation on solar cycle timescales of solar irradiance in the 4-27 nm region.

These suggestions can be confirmed by higher spectral resolution observations that will be made on the Solar Dynamics Observatory mission.