4-17 September 2005
Solar Storm Period

During the first half of September 2005, a period of increased solar activity occurred that rivaled the number and magnitude of flares produced during the "Halloween" storm in October-November of 2003. The presence of NOAA active region 808 produced a total of 115 flares of GOES C-class or higher, including 26 M-class and 10 X-class flares (see Figure 1 below). The largest of the flares, a GOES X17.0 flare that occurred on September 7, 2005, was the largest flare that has occurred since the X28+ flare on November 4, 2003, and was just smaller than the X17.2 flare that occurred on October 28, 2003. This X17.0 flare was the 4th largest observed X-ray flare since GOES started making flare observations in 1986.

Many of the flares that occurred during this storm period were observed by SORCE at various stages of the flare evolution. The large X17.0 flare was observed by both the TIM and XPS instruments aboard SORCE as shown in Figures 1 and 2.

The irradiance observations of the solar flares during this storm period add to the solar flare data set already obtained by SORCE and are helping researchers to determine the temporal and spectral evolution of the irradiance changes during a solar flare. The knowledge gained from this research has far reaching implications ranging from solar and flare physics to atmospheric applications.

Figure 1. SORCE XPS 0.1-7 nm and GOES XRS 0.1-0.8 nm time series
during the September 2005 solar storm period.
Note that Sept. 1 is DOY 244.

Figure 2. Variation of the total solar irradiance (TSI) during the X17 flare on 7 Sept. 2005.