Solar storms make a comeback

Jan. 23, 2002  — Just when you thought the sun was maxed out, scientists say they’ve detected a second peak in the 11-year cycle of solar activity. Such flare-ups of solar “weather” can create problems for satellites in orbit and power grids on Earth — and the latest double peak demonstrates how complex those weather patterns can get.

THE SUN may seem unchanging to the casual observer, but astronomers have found that it throws off an electrically charged stream of particles that ebb and flow over the course of days and years. Every 11 years, the stream rises to a peak known as the solar maximum, or “Solar Max” — a time when unexpected bursts can become downright dangerous.

During the Solar Max of 1989, an outburst interacted with Earth’s magnetic field and overloaded circuits on an electrical power grid in Quebec, creating a blackout for the 6 million people served by that grid. Geomagnetic storms have also taken out satellites, disabling pager services and upsetting TV broadcasts.

So there was a huge sigh of relief in 2000 when scientists saw signs that the latest Solar Max had come and gone, a bit earlier than expected. That year’s biggest outburst was the “Bastille Day Event” of July 14, which killed off a Japanese X-ray satellite and temporarily disabled other spacecraft.

That sigh may have been premature, however: Over the past couple of months, solar scientists have seen a resurgence in sunspot activity and radio emissions. In fact, the solar radio flux was significantly stronger in December than it was in mid-2000.

“The current solar cycle appears to be double-peaked,” said David Hathaway, a solar physicist at NASA’s Marshall Space Flight Center.

‘IT’S NOT OVER’

The double peak doesn’t exactly come as a surprise, said Paal Brekke, the European Space Agency’s deputy project scientist for the Solar and Heliospheric Observatory: The two preceding Solar Maxes also exhibited a double peak.

Brekke and Hathaway cautioned that the rise and fall of solar activity is never as smooth as the bell curves that accompany scientific forecasts. Although the pattern is still generally consistent with an 11-year cycle, the detailed picture won’t become clear until the complete cycle is charted.

“The jury’s isn’t in on this,” Hathaway told MSNBC.com Wednesday. “If we continue to have big numbers, we may actually end up with a peak this time that’s a little bigger than the earlier one.”

Even passing the double peak won’t bring a lull in the space weather, scientists say.

“The statistics show that in the decaying phase (of the solar cycle), you have the biggest and most powerful flares,” Brekke told MSNBC.com.

Coronal mass ejections — the “storms” of charged particles thrown off by the sun — also tend to pack more of a punch after Solar Max has passed, Brekke said. In the decaying phase, such storms tend to have what’s known as a southward magnetic component, which interacts more strongly with Earth’s magnetic field.

Based on past research, the active phase on the other side of Solar Max could last two to four years, Brekke said.

“Basically, it’s not over,” he said of the outlook for solar activity. “It’s sometimes the most interesting phase. It also means that this winter and also probably next winter will be great for aurora sightings.”

He explained that sky watchers can watch the charts and dials in the “Space Weather” section of the SOHO Web site to determine when the conditions are right for geomagnetic storms to spark widespread Northern or Southern lights. The National Oceanic and Atmospheric Administration’s Space Environment Center also provides up-to-date forecasts for solar weather.

PREDICTING THE WEATHER

The sun’s double peak serves as just one more illustration of how variable our seemingly constant energy source can be. Hathaway noted other cycles of variability: For example, Earth-directed explosions tend to occur every 27 days — the time it takes for sunspots to rotate once around the sun. Occasionally, there’s a mysterious 155-day cycle of solar flares. And an analysis of the sun’s “seismic waves” has indicated that currents of gas within the star speed and slacken every 16 months.

“That’s about the same as the time between the double peaks of recent solar maxima,” Hathaway told the Science@NASA Web site, although he cautioned that “it’s hard to be sure” whether the double peaks could be linked to the sun’s internal ebb and flow.

A NASA sun-observing satellite called the High Energy Solar Spectroscopic Imager, whose launch has been delayed for a year and a half, should provide valuable insights, Hathaway told MSNBC.com. “We’re hoping its going to launch in the next couple of weeks, and it wants to see big flares,” he said.

Predicting solar weather isn’t just an academic exercise, Brekke said. Researchers are trying to develop a reliable early warning system so that the people managing satellite systems and electrical grids can get two or three days’ notice of potential disruptions. Even the intelligence satellites monitoring the war on terrorism can be affected by the sun’s radio outbursts, Brekke noted.

“That’s one of the reasons why the military is looking at this early warning system,” Brekke said.

An earlier version of this report misstated the timing of the Bastille Day Event.

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