Coronal Holes and Aurora (October 8, 2003)
Hi-res TIF image (1.7M)
Hi-res TIF image (5.3M)
This week the Sun had a good-sized coronal hole that rotated into a
position on the right side of the Sun where it could have generated
aurora on Earth. Coronal holes, which appear as darker areas in
SOHO's ultraviolet imagers, are a source of the higher speed solar
wind. The magnetic field in coronal holes opens outward, allowing
electrically charged particles to escape and be accelerated by the
solar wind. Elsewhere in the Sun's outer atmosphere, the magnetic
field curves back toward the surface and traps nearly all charged
particles close to the Sun. The density and speed of the solar wind
coming from coronal holes are significantly higher than in the solar
wind originating over "closed" magnetic field regions.|
When these "high speed streams" from coronal holes sweep past the earth, the charged particles interact with the atoms and molecules of the gases in the Earth's upper atmosphere, leading to the auroral glow. October is usually a good time to look for auroras, so our friends in Canada and other higher latitude regions like the northern tier states of the U.S., keep your eyes to the skies!
The movie from EIT (in fourteen times ionized iron) shows solar activity and the coronal hole as it rotates around almost to the Sun's edge. The auroral image was taken near Québec this summer by Michel Tournay. Thanks for sharing it with us, Michel!
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