Flare Variability of the Solar XUV Irradiance from the SORCE XPS

Tom Woods [tom.woods@lasp.colorado.edu] and Greg Kopp, Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder.

The SORCE satellite was launched in January 2003, and the solar activity has evolved from near solar maximum conditions to moderately low activity during the SORCE mission in 2005. The XUV Photometer System (XPS) aboard SORCE measures the soft X-ray, or XUV, energy input to Earth's atmosphere. The XPS instrument is measuring the solar XUV irradiance with 7-10 nm resolution shortward of 34 nm and the bright hydrogen emission at 121.5 nm. The SORCE XPS instrument is best known for observing over 800 flares, with each lasting from minutes to hours. The XUV radiation, being mostly from coronal emissions, varies more than other wavelengths in the solar spectrum. The XPS measurements indicate variations by a factor of 50 for the largest flares during the October-November 2003 solar storm period and that the XUV variations can be as much as 20% of the total flare energy as determined from the total solar irradiance (TSI) measurements by SORCE TIM. The flare variations of the solar XUV irradiance will be discussed in the context of the SORCE mission.