lunedì 21 novembre 2016

BIG CORONAL HOLE

RETURN OF THE BIG CORONAL HOLE: At the end of October, a hole in the sun's atmosphere lashed Earth's magnetic field with solar wind, sparking moderately-strong geomagnetic storms and almost a full week of Arctic auroras.  News flash:  It's back.  The same "coronal hole" is turning toward Earth again. NASA's Solar Dynamics Observatory photographed the structure on Nov. 20th:
Coronal holes are regions in the sun's atmosphere where the magnetic field peels back and allows solar wind to escape.  Since our last encounter with this hole in late October it has been transiting the farside of the sun, carried around by the sun's 27-day rotation.  Now that it is back we can see that the hole is not quite as large as it was a month ago--but it is still impressive, covering almost 1/3rd of the visible solar disk.
NOAA forecasters expect the leading edge of the emerging solar wind stream to reach Earth on Nov. 22nd, bringing with it a chance of G1-class geomagnetic storms.  Stay tuned!  Free: Aurora Alerts.

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