Observations of the Sept. 2005 solar storm

September 17, 2005

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, 2003, 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 SEE at various stages of the flare evolution, even though SEE only observes the Sun for approximately 3 minutes out of every 96 minutes. The observation of the large X17.0 flare by SEE unfortunately did not occur until 56 minutes after the gradual phase peak, but the M3.0 flare on September 11th was observed 3 minutes after the gradual phase peak and the X1.7 flare on September 13th (see Figure 2 below) was observed just 9 minutes after the peak of the gradual phase. Three other large flares, the X1.1 on September 9th, an M4.1 on September 10th, and the M3.5 on September 16th were observed minutes prior to the peak of the gradual phase, allowing observations of the impulsive phase of the flare that can provide irradiance increases of 3-4 times those of the gradual phase increases in particular emission formed in the transition region from 60-155 nm.

The spectrograph observations of the solar flares during this storm period adds to the first-of-its-kind solar flare data set that is helping researchers to determine the temporal evolution of the irradiance changes in the VUV wavelengths (0.1-195) during a solar flare. The knowledge gained from this research has far reaching implications ranging from solar and flare physics to space weather applications.

Flares Sept 05
Figure 1. TIMED SEE 1-7 nm (divided by 10,000) and GOES XRS 0.1-0.8 nm time series during Sept. 2005 solar storm period.
Flare 13 Sept. 05
Figure 2. Irradiance variation for the X1.7 flare on 13 Sept. 2005.
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