Variability of the Solar XUV Irradiance from the SORCE XPS

Tom Woods [tom.woods@lasp.colorado.edu] and Gary Rottman, LASP, Univ. of Colorado

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 2004. 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 solar irradiance varies on all time scales, seconds to years, and this variation is very dependent on wavelength. During the SORCE mission, the XPS instrument has observed several hundred flares which last from minutes to hours and over 20 solar rotations which have a period of about 27 days. 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 a factor of about 2 for solar rotation. The variations of the solar XUV irradiance will be discussed in the context of the SORCE mission.