"on the loose"

 

BUTTERFLY-SHAPED HOLE IN THE SUN'S ATMOSPHERE: A hole has opened in the sun's atmosphere, and it is venting a stream of solar wind toward Earth. NASA's Solar Dynamics Observatory photographed the 500,000-km-wide butterfly-shaped gap on Sept. 11th:

This is a "coronal hole" -- a region in the sun's atmosphere where magnetic fields open up and allow solar wind to escape. Coronal holes look dark because hot plasma normally contained there is missing. The gaseous material is "on the loose" and on its way to Earth.

A stream of solar wind flowing from this coronal hole should reach Earth on Sept. 14th. Its arrival could spark G1 to G2-class geomagnetic storms. The odds of storming are increased by the "Russell-McPherron effect," which links the magnetic fields of the sun and Earth during weeks around equinoxes.