Double "halo" coronal mass ejections (November 27, 2001)
This single image from 23 November 2001 shows a 'full-halo' coronal
mass ejection (CME) exploding out from the Sun and beginning to
overtake another halo CME that erupted just hours before it. The
first CME is seen as a faint whitish cloud in the lower right
quadrant of the image. The image, taken by the LASCO C3 instrument,
shows the expanding clouds of particles in visible light. A "halo"
CME expands from the Sun in all directions, and is either heading in
Earth's direction or directly away from it. The charged particles did
strike the Earth's magnetosphere in only 27 hours, which implies a
mean speed of something like 1500 km/s. It did generate strong aurora.|
Because the shock front from this event was so dense and fast, calculations show that it should have compressed the magnetosphere by about a factor of two, the most pressure measured by SOHO's proton monitor. Below, the CELIAS chart of this event:
The large number of white streaks on the C3 image are evidence of particle strikes on SOHO's imager. These are high-energy protons that were blasted into space by a solar flare detected at 22:32 UT, about the time of the first CME.
For more on large proton events check this "Shocking Events" Hotshot.