Thursday, November 5, 2015

Coronal holes


 
Coronal holes appear as dark patches on the Sun, primarily in extreme ultraviolet and soft X-ray images due to the lower plasma density and electron temperature compared to the surrounding quiet Sun. Coronal holes form over open magnetic flux regions where one end of the magnetic field lines is attached to the Sun and the other end is dragged outward into interplanetary space by the solar wind.

The solar wind which is magnetized plasma of ions and electrons can flow out along these open field lines at very high speeds. Coronal holes occur usually at the solar poles (poloidal magnetic field), but during more active periods these dark holes can exist at all heliolatitudes and can trigger geomagnetic storms.


Know more:
https://www.cfa.harvard.edu/~scranmer/Preprints/eaaa_holes.pdf
https://www.cfa.harvard.edu/~scranmer/ITC/eaaa_solar_wind_schwenn.pdf

Image via Solar Dynamics Observatory/NASA

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