A better way to forecast storms ... on the sun

The ability to predict the sunspot cycle just got better - a boon for electricity customers and future space travelers.

Sometimes all it takes to ruin a trip is a spate of bad weather - even if the travel is via spaceship and the destination is the moon or Mars.

The sun occasionally hurls hailstorms of energized particles at speeds of up to several million miles an hour. These can threaten astronauts' health and the electronic gear on which they rely.

Now, scientists say they have devised a more accurate way to forecast the onset and relative strength of the sun's stormy "seasons," or sunspot cycles, which peak roughly every 11 years. Some liken the approach to seasonal hurricane forecasts on Earth - but with potentially much higher accuracy.

Most immediately, researchers say, the technique could help satellite operators avoid breakdowns in communications and navigation services. It should also help electric utilities prepare for intense solar storms, which have triggered blackouts in the past by sending unexpectedly large currents surging through power lines.

Eventually, they say, the approach will help mission planners figure out the best time to plan for "outdoor" activities on the moon or schedule interplanetary trips.

Typically, the most sought-after information is when the next cycle will start, and its strength, duration, and probable effects, says Joseph Kunches, who heads the forecast and analysis branch at the Space Environment Center in Boulder, Colo., which is part of the National Oceanic and Atmospheric Administration.

Forecasters have replied, in effect: We'll get back to you on that. Scientists didn't know enough about sunspot cycles to give forecasters the help they needed. That's why Dr. Kunches says his team is "very excited about this work.... It's going to help us answer some difficult questions that users of space services ask us all the time."

Until now, sunspot forecasts were based mostly on statistics drawn from historical cycles. The new approach incorporates the sun's basic physical processes that underlie the cycles.

A strong one headed Earth's way

For the record, the team's research indicates that the next sunspot cycle will be 30 to 50 percent stronger than the last one, not weaker as others have forecast. The cycle will start late in 2007 or early in 2008, six to 12 months behind schedule, and it should peak in 2012, the researchers say. In testing their model against the past 12 solar cycles, the team reproduced "forecasts" with better than 98 percent accuracy.

Scientists already knew that the sun is a blowhard, constantly shedding electrons and hot, electrically charged gas. These billow from the star as solar wind. Solar storms, driven by the sun's magnetic fields, turbocharge this wind. In some cases, the magnetic fields become increasingly distorted, trapping more and more matter from the sun's atmosphere inside them. When the field reaches the breaking point, it explosively hurls the material into space at millions of miles an hour. In other cases, solar flares erupt, releasing enormous amounts of radiation. These tend to happen near sunspots - regions where magnetic fields are very dense. In all, astronomers have identified four types of eruptions that keep technologists up at night.

In the new research, unveiled this week by Mausumi Dikpati of the National Center for Atmospheric Research's High Altitude Observatory in Boulder, the scientists looked at the flow of hot gases, or plasma, in the outer layer of the sun's interior. Sunspots appear to be tied to the activity of magnetic fields set up as this plasma "conveyor belt" flows from the sun's poles to the equator, rises to the surface, then heads back. The team traced the timing between sunspot cycles to the speed of the conveyor. The strength of a cycle's peak is tied to the strength of another magnetic field the process sets up along the equator.

A 150-year-old question is settled

So far, the team has tested its model against the last eight sunspot cycles, with what colleagues say are impressive results.

The results are exciting because they appear to settle "the 150-year-old question of what causes the 11-year sunspot cycle," says David Hathaway, a solar astronomer with NASA's Marshal Space Flight Center in Huntsville, Ala. His one quibble: His own work suggests that the next sunspot cycle will start sooner - late this year or early next - although he agrees with Dr. Dikpati's assessment that it will be a strong one.

"We're anxiously awaiting the appearance of those first spots from the new cycle" to see who is right, he says.

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