Holes in Earth's magnetic cloak let the sun in

By Clare Baldwin

SAN FRANCISCO (Reuters) - The Earth's protective magnetosphere has two large holes that are letting in disruptive solar winds, scientists said on Tuesday.

Understanding how these holes form will help them better predict the electrical storms that cause power grid blackouts and the aurora, activity that will peak in 2012 as sunspots hit their maximum level.

Scientists at the American Geophysical Union meeting in San Francisco said they had been entirely wrong about how solar particles that cause the storms were entering the Earth's magnetosphere.

The magnetosphere is a bubble of magnetism that surrounds Earth and protects us from solar wind.

Scientists once believed that the particles entered when the sun's magnetic field was aligned opposite to that of the Earth's. But findings presented at the meeting show that 20 times more solar particles enter the Earth's magnetic field when it is aligned in the same direction as the sun's magnetic field.

The alignment causes the two magnetic fields to connect and tears holes in the Earth's magnetic field over the poles.

"What we observed was the breach in the levee," said Jimmy Raeder, a physicist at the University of New Hampshire. "This has taken us completely by surprise."

In June 2007, NASA's five THEMIS spacecraft probes flew through one of the tears just as it was opening. Sensors recorded a torrent of solar wind particles streaming into the magnetosphere, said Raeder.

"The opening was huge -- four times wider than Earth itself," said Raeder. "This kind of influx is an order of magnitude greater than what we thought was possible."

Most of the particles are deflected back into space, but some circulate in the magnetosphere, get energized, and cause electrical storms that trigger power grid outages, cause problems for aircraft flying over the poles, and can damage satellites in geosynchronous orbit.

"There's a bigger risk because we have more stuff in space now," said Raeder.

Scientists said that the majority of solar storms take place midway through and on the tail end of the solar cycle. This 11-year cycle of activity is at its minimum now and electrical storms will be at their peak in 2012.

(Editing by Maggie Fox, Editing by Sandra Maler)