Sun Entering Weakest Cycle Since 1928

NOAA releases new predictions for solar cycle.

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By Solmaz Barazesh, Science News

The sun has entered its weakest cycle of magnetic activity since 1928, meaning fewer solar flares and coronal mass ejections, scientists predicted in a May 8 teleconference. A panel of solar scientists assembled by the National Oceanic and Atmospheric Administration’s Space Weather Prediction Center reports that the cycle, which scientists believe began in December 2008, will peak in May 2013.

Storms of solar magnetic activity cause flares and ejections that can spit X-rays, UV light and billions of tons of charged particles into space, and toward Earth. These outbursts can make Earth’s upper atmosphere expand, potentially knocking out electrical grids and disrupting satellite communications — and can harm spacewalking astronauts.

“It’s fair to say we probably won’t see a whole lot of solar storms from this cycle,” Douglas Biesecker of NOAA’s Space Weather Prediction Center in Boulder, Colo., said at the teleconference. “But a weaker cycle won’t lessen the intensity of the storms, just the number of them.”

Scientists use the number of sunspots, blotches of concentrated magnetic activity on the surface of the sun, as a measure of solar activity. The panel predicts the next solar cycle, cycle 24, will average 90 sunspots per day at its peak, lower than the 120 sunspots a day expected for a more typical cycle. The predictions are based on cycle 24’s slow start.

The new predictions update a 2007 NOAA solar cycle report. In 2007 the panel split, with some scientists forecasting a moderately strong cycle 24 and others calling for a weaker cycle. Both groups thought cycle 24 would be well underway by now, peaking in 2011.

But the transition from sun cycle 23 to 24 was not what anyone expected. Solar magnetic activity usually ebbs and flows in cycles that last about 11 years. As one cycle sinks to a minimum of activity, the next cycle begins. The panel consensus is that cycle 23 finally reached its sunspot minimum in December 2008, almost 13 years after it began, Dean Pesnell of NASA’s Goddard Space Flight Center in Greenbelt, Md., said at the teleconference.

The first sunspots from cycle 24 were seen in December 2008, but a recent lull in sunspots shows that cycle 24 is starting slowly. Pesnell said that in the past, when early activity has been low, the cycle has tended to have little activity overall.

“Usually, when a new sun cycle starts, it takes off pretty quickly. This one is just chugging along,” comments David Hathaway of NASA’s Marshall Space Flight Center in Huntsville, Ala.