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The figure shows the onset of the SEP event as seen by GOES 8 and SAMPEX; four polar cap traversals by SAMPEX are shown. Around 36000 sec UT SAMPEX saw a polar cap population of only the GCR. The onset of the SEP occurred just before SAMPEX entered the polar cap the next time at 38200 sec UT. Note that SAMPEX shows the effect of velocity dispersion: the flux of higher energy protons exceeded the lower energy ones during the first polar cap traverse. The lower energy GOES 8 channels are responding to higher energy protons. The next two SAMPEX polar cap crossings show that the spectral inversion disappeared and, whereas the > 85 MeV protons had peaked, the 18-65 MeV proton intensity continued to rise.
Above is background material for archival reference only.