NOAA forecasts a mild solar season
Good news for communications systems, though a severe storm could still occur
- By William Jackson
- May 14, 2009
As the sun enters a new cycle of solar activity, an international panel of experts predicted that the coming solar storm season will be milder than usual, with fewer sunspots on average and fewer solar storms battering the Earth’s magnetic field and atmosphere.
Those high-energy eruptions from the sun can interfere with satellite-based and terrestrial communications and power distribution, damage satellites, and pose a threat to astronauts.
The National Oceanic and Atmospheric Administration’s Space Weather Prediction Center released the forecast this month, and it is welcome news for the operators of the Earth’s electronic infrastructures and those who depend on them. But severe storms remain a threat.
“As with hurricanes, whether a cycle is active or weak refers to the number of storms, but everyone needs to remember it only takes one powerful storm to cause huge problems,” said Douglas Biesecker, a solar physicist at NOAA and chairman of the panel. “The strongest solar storm on record occurred in 1859 during another below-average cycle.”
That storm shorted out telegraph wires, caused fires in North America and Europe, and produced northern lights bright enough to read by, according to NOAA.
In the 150 years since then, society has become increasingly dependent on space-based communications and other electronics. A strong solar storm has the potential to knock out commercial communications satellites and swamp Global Positioning System signals. Cellular phone signals could be affected, and routine transactions from automated teller machines and credit card terminals that rely on satellite links could be disrupted.
If a storm is severe enough, it could even damage physical infrastructure. In a recent study, the National Academy of Sciences found that if a storm as severe as the one in 1859 occurred today, it could cause as much as $2 trillion in damages and require four to 10 years for recovery, compared with the estimated $125 billion in damages Hurricane Katrina caused.
Solar cycles last about 11 years on average and are defined by sunspots, areas of highly organized magnetic activity on the sun’s surface. Sunspots are characterized by their polarity, which reverses with each new solar cycle. At the beginning of a cycle, they typically appear first in the higher latitudes near the solar poles and over time begin to appear closer to the solar equator. Sunspot activity peaks in the middle of a cycle.
In 2007, the Space Weather Prediction Center said the current cycle, identified as Solar Cycle 24, would begin in early 2008 and peak in late 2011 or early 2012. At the time, scientists were split on whether the new cycle would be severe or mild.
The first sunspot of Cycle 24 appeared in January 2008, but sunspot activity from Cycle 23 wound down more slowly than expected. That lull, which stretched Cycle 23 to an unusual 12 years and seven months, convinced forecasters that the new cycle would be mild. Cycle 24 now is expected to peak in May 2013 with an average of about 90 sunspots a day.
“We see Cycle 23 and 24 sunspots overlapping, and we expect to for a number of years,” Biesecker said. “That’s normal.”
Reading solar cycles is an art and a science. Scientists use a combination of statistical techniques and models for leading indicators in observing sunspots and other solar magnetic activity. Although sunspots from different cycles overlap, one cycle is said to begin when the average activity of the preceding one peters out.
“It’s like detecting when a recession starts or ends,” Biesecker said. “You have to look back.”
Infrastructure operators, including the Defense Department, use the Space Weather Prediction Center’s forecasts and reports to plan activities. One critical area is planning the life cycle of satellites, which are affected by the electromagnetic beating they take from storms and the increased drag created in a highly charged atmosphere.
“The higher the activity in the cycle, the faster the satellite will fall out of orbit,” Biesecker said.
William Jackson is a senior writer of GCN and the author of the CyberEye blog.