High speed solar wind particles from a large coronal hole are buffeting Earth's magnetosphere.

The end of February could mark another good weekend for aurora watchers, thanks to a large coronal hole currently straddling the visible disk of the sun. High speed solar wind particles streaming out of the hole reached the Earth today and began to buffet our planet's magnetosphere. Space weather forecasters expect moderate to high levels of aurora borealis with minor impacts on satellite operations and high latitude power grids for the next few days.

Coronal holes are easy to spot by looking at the Sun through an x-ray telescope. They appear as very dark areas that contrast with bright spots overlying sunspot groups. Hot gas around sunspots is captured by magnetic fields that rise up out of one sunspot and bend back to reconnect at another spot nearby. These glowing 'magnetic bottles' shine brightly at x-ray wavelengths.

The magnetic fields around coronal holes are different. Instead of looping back to reconnect on the sun's surface, these magnetic fields are essentially open. They extend far out into the solar system and no one knows exactly where they reconnect. Rather than trapping the hot gas, the open field lines of a coronal hole allow high-speed solar wind particles to escape.

The solar wind flows away of the Sun in all directions, not just from coronal holes, but the wind speed is high (up to 800 km/s) over coronal holes and much lower (300 to 400 km/s) elsewhere. The higher pressure streams from coronal holes squeeze the Earth's magnetic field and can produce geomagnetic activity.

The coronal hole visible on the sun now is at least 7 months old. It has been seen by the Yohkoh soft x-ray telescope during each of the past seven solar rotations. (The sun rotates on its axis once every 27 days.) After this apparition, there is every reason to expect its return 27 days hence for another bout of solar wind gusts and geomagnetic activity.

It's not yet clear how much activity will result from this week's coronal hole. The Geophysical Institute at the University of Alaska predicts:

"Auroral activity will be high today (February 23). Weather permitting, highly active auroral displays will be visible overhead from Barrow to Anchorage, and visible low on the horizon from Bethel, Soldotna and southeast Alaska."

Mitch Battros
Producer - Earth Changes TV
http://www.earthchangesTV.com