From the ABC 7 Weather team

Solar flare 2011: Why is predicting space weather so hard?

February 18, 2011 - 01:15 PM
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The sun, today. (NOAA/SWPC)

The sun has just burped out a medium-sized M-class solar flare, not quite as huge as the Jupiter-sized X-class eruption earlier this week but still a clear sign that the star is ramping up its explosive 11-year cycle. All these tears in the sun’s atmospheric fabric are showering earth with billions of tons of charged particles.

What have been the consequences? Millions without power? Computer crashes causing stock market panic?

Not quite. The National Weather Service in Sterling, Va., reports one radio down. But it appears to be a land issue, not a space one, and Verizon is on the way.

Over in Boulder, Colo., NOAA’s Space Weather Prediction Center is carefully monitoring the solar storm, and so far the impact looks minimal. While NOAA initially predicted G2 to G3 magnetic storm activity, which can cause widespread radio blackouts and fry power-company equipment, sensors have only picked up G1-level disturbances. But it could have been a lot worse; skip below for the reason.

The biggest problem the X-class solar flare caused was when it beaned the earth with radiation on Monday a few minutes after the flare erupted, which resulted in the strongest radio blackout in four years. The sunlit areas of the earth experienced high-frequency radio disruptions; China reported dead radios and some airplanes over the Pacific also had silent radios for about 20 minutes. But airlines have protocols that go into place during solar outbursts. Planes continued on course and no major trouble was reported.

The bulk of the flare’s output – clouds of charged plasma known as coronal mass ejections – are washing ashore on our planet today. The resulting geomagnetic storm has the weather equivalent of an Alberta Clipper, that is to say, not much power.

“The effects been pretty minor, to be blunt,” says Joe Kunches of the SWPC. But they could have been big. That’s because CMEs have an unpredictable quirk in their magnetic fields that can dramatically alter the force of their impact.

When the sun shoots off a CME, a cloud of charge emerges that also has a magnetic field. The field can have an orientation of north or south. For some reason, when it is south the effect of the CME is much more pronounced on earth.

“We found that if the field in the magnetic cloud is southward, then the energy transfer from the ejecta to [the earth’s own magnetic] field is the most efficient it could be,” says Kunches. Then the earth’s magnetic field is really stirred up, and we see a strong magnetic storm.

But if the CME’s magnetism is oriented northward, the result is like “a little punch in the nose, a dynamic pressure pulse,” says Kunches. “The earth rings a little bit, and the magnetic storm is nowhere near as severe.”

But the incoming plasma clouds don’t reveal their orientation until the last moment, and the orientation switches back and forth regularly.

“It could be a flip of the coin. In this event, the thing went by at 8 p.m. [EST], and it’s still kind of going by as an elongated structure. And within that structure, the magnetic field has probably flipped back maybe 20 times,” Kunches says. Thankfully, “most of the field in the cloud that went by the earth was northward.”

One of the main challenges in the space weather-prediction field is grappling with the changing polarities of CMEs. Kunches likens it to the old Harlem Globetrotters gambit, where a player ran up and threw a bucket filled with either feathers or water on some poor soul. “It’s feathers northward, and water southward,” he says.

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