Monday, November 24, 2008

Coronal holes

Coronal holes are variable solar features that can previous for weeks to months. They are big, dark areas when the Sun is viewed in x-ray wavelengths, sometimes as large as a district of the Sun’s surface. These holes are entrenched in large cells of unipolar magnetic fields on the Sun’s surface; their field lines make bigger far out into the solar system. These open field lines allow an incessant outflow of high-speed solar wind. Coronal holes have a long-term cycle, but the cycle doesn’t correspond precisely to the sunspot cycle; the holes tend to be most many in the years following sunspot maximum. At some stages of the solar cycle, these holes are incessantly visible at the solar north and south poles.


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