As sun flips polarity, scientists are bemused

Posted by Emma Woollacott

The sun is well into a flip in polarity - with its north and south poles swapping places - but the process isn't going as expected, scientists say.

Every 11 years or so, around solar maximum, the magnetic field on the sun reverses completely. At the moment, though, the polarity at the north of the sun appears to have dropped close to zero, while the polarity at the south is only just beginning to decrease. It had previously been assumed that both polarities switched at the same time.

"Right now, there's an imbalance between the north and the south poles," says Jonathan Cirtain, NASA project scientist for Japan's Hinode solar mission.

"The north is already in transition, well ahead of the south pole, and we don't understand why."

Daikou Shiota, a solar scientist at RIKEN Institute of Physics and Chemical Research, and his team used Hinode's high resolution Solar Optical Telescope  to observe the magnetic map of the poles every month since September of 2008.

Early maps showed large, strong concentrations of magnetic fields that were almost all magnetically negative in polarity. Recent maps, however, show a different picture.

Not only are the patches of magnetism smaller and weaker, but now there is a great deal of positive polarity visible as well. What once pointed to a strongly negative north pole, is now a weakly magnetized, mixed pole that will become neutral - which occurs at solar maximum - within the month, according to the team's predictions.

"This is the first direct observation of this field reversal," says NASA space scientist Jonathan Cirtain. "And it is extremely important to understanding how the sun's magnetism generates the solar cycle."

Typical models of the magnetic flip suggest that as active regions rotate around the equator, their higher, trailing edge - which is almost always the opposite polarity from the pole in their hemisphere - drift upward, eventually dominating the status quo and turning positive to negative or negative to positive.

But the Hinode data show that this transition at the north began before such drifting had a chance to occur.

"This is one of the most interesting things in this Hinode paper to me," says principal investigator for Hinode's Solar Optical Telescope Ted Tarbell.

"How did the polar reversal start so early, even though the onset of the solar cycle, that is, increased activity at lower latitudes, hadn't begun yet?"