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Laboratory for Atmospheric and Space Physics

Science Results

SORCE XPS has produced stunning new observations of irradiance increases in solar flares, at longer wavelengths than the NOAA GOES routine monitoring in the 0.05 to 0.8 nm range. Dramatic solar storms – including some of the largest in the space era – occurred during the SORCE mission, for example in May-June 2003, October-November 2003, July 2004, November 2004, January 2005, September 2005, and December 2006. The October-November 2003 storms produced record solar flares with the X28 flare on November 4, 2003 and the X17 flare on October 28, 2003. The XUV variations during these large flares are larger than that expected for solar cycle variations for the XUV range, and this finding represents one of the most important results from the XPS measurements. Furthermore, the simultaneous observations with the SORCE and TIMED SEE instruments have provided new insight into the first definitive flare detection in the TSI record by TIM and the spectral irradiance variability during flares over the full UV range from 0.1 nm to 200 nm as shown in Figures 1 and 2 below [Woods et al., 2004]. Additionally, the TIM and XPS measurements of several flares indicate that the total energy from the flares are about 10 times larger than previous estimates [Woods, Kopp, and Chamberlin, 2006].

Figure 1. Time series of solar irradiance measurements during the X17 flare on 28 October 2003. The flare increase is taken between the peak value and the pre-flare value, being about 10:30 UT for the UV emissions and about 9:30 UT for the X-ray emissions. The time derivative of the GOES X-rays (blue line) is an estimate for the hard X-ray time series (impulsive phase of flare). Figure is from Woods et al. 2004.

Figure 2. Flare and pre-flare solar irradiance ratios for the X17 flare on 28 October 2003 in 3 spectral ranges. The lower curves in each panel are the flare spectra on a log scale to clarify the spectral features. Figure is from Woods et al. 2004.