Solar storms tend to occur near sunspots, cool regions on the sun's surface that appear as dark blotches. Scientists believe the spots result from concentrated magnetic fields inside the sun.
The number and intensity of sunspots fluctuates over time, reaching a peak about every 11 years. This 11-year pattern is known as the solar cycle.
Joseph Kunches, chief of the forecast and analysis branch of the National Oceanic and Atmospheric Administration's Space Environment Center in Boulder, equated the space weather forecast to the annual hurricane forecast.
"The kinds of questions that are posed to hurricane forecasters also come to us in terms of space weather," he told reporters.
"When is the next cycle going to start? How strong will it be? When will it quiet down? And compared to, say, the last [cycle in] recent memory, what are the effects going to be?"
The new forecast draws on new understanding of how plasma currents in the sun's interior generate sunspots and the related solar storms. These plasma flows transport, concentrate, and help spread out solar magnetic fields.
Two major plasma flows govern the cycle, the researchers said.
The first, known as the meridional flow pattern, circulates between the sun's equator and its poles over a period of 17 to 22 years and acts like a conveyor belt of sunspots. The flow transports imprints of sunspots that occurred over the previous two sunspot cycles.
This imprint is carried into the interior, where scientists believe the sunspot-producing magnetic fields are generated. New sunspots form based on the imprints created during the most recent cycle.
The second flow results from the sun rotating faster at the equator than it does near the poles. This periodically concentrates the solar magnetic field at the equator, leading to peaks in solar storm activity, the researchers said.
The team expects the next cycle to begin in late 2007 or early 2008, which is about 6 to 12 months later than the cycle would normally start. The researchers' model shows the plasma circulation has slowed down during the current cycle.
David Hathaway, a solar astronomer with NASA's Marshall Space Flight Center in Huntsville, Alabama, said that models used by him and his colleagues to predict the next solar cycle agree with the greater activity predicted by Dikpati's model.
But Hathaway differs on the timing.
According to Hathaway's team's analysis of past solar cycles, intense cycles are preceded by shorter cycles. This would suggest that the next cycle will start by the end of this year or early next year.
"At this point, we are anxiously awaiting the appearance of those first spots from the new cycle," Hathaway said at the briefing.
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