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Solar Cycle 24 May Have “Double Peaks,” Says NASA Solar Physicist


According to NASA, the current solar cycle -- Solar Cycle 24 -- should hit its “solar max” sometime in this year, but so far, solar activity has been relatively low. According to an article by NASA’s Dr Tony Phillips, this period of quiet has led some observers to wonder if forecasters missed the mark. But solar physicist Dean Pesnell of NASA’s Goddard Space Flight Center has a different explanation: “This is solar maximum. But it looks different from what we expected because it is double peaked.” Pesnell noted similarities between the current cycle and Solar Cycle 14, which happened between February 1902 and August 1913 and experienced a double peak. If the two cycles are in fact twins, he said that “it would mean one peak in late 2013 and another in 2015.”

Solar activity tends to swing back and forth: At one end of a solar cycle, there is a quiet time with few sunspots and flares, while at the other end, solar max brings high sunspot numbers and solar storms. Even so, astronomers -- who have been counting sunspots for centuries -- have noticed that a solar cycle is not perfectly regular, with the swing in sunspot counts taking anywhere from 10-13 years to complete. In addition, the amplitude of each cycle can and does vary, with some solar maxima being very weak (such as Solar Cycle 6), while others can be very strong (such as Solar Cycle 19).

“The last two solar maxima, around 1989 and 2001, had not one but two peaks,” Pesnell explained. Phillips’ article explained how “solar activity went up, dipped and then resumed, performing a mini-cycle that lasted about two years.” Pesnell said that the same thing could be happening now. Even though sunspot counts jumped in 2011 and dipped in 2012, he said he expects them to rebound again in 2013: “I am comfortable in saying that another peak will happen in 2013 and possibly last into 2014.”

According to Phillips, solar activity in the Sun’s hemispheres does not always peak at the same time. “In the current cycle, the south has been lagging behind the north,” he said. He explained that if a second peak occurs, it will likely feature the Sun’s southern hemisphere displaying a surge in activity.

Pesnell is a member of the NOAA/NASA Solar Cycle Prediction Panel, a group of solar physicists that assembled in 2006 and 2008 to forecast the next solar max. “At that time, the Sun was experiencing its deepest minimum in nearly a hundred years,” Phillips’ article explained. “Sunspot numbers were pegged near 0 and x-ray flare activity flat-lined for months at a time.” The panel issued the following statement at the time, explaining its prediction:

“The Solar Cycle 24 Prediction Panel has reached a consensus. The panel has decided that the next solar cycle (Cycle 24) will be below average in intensity, with a maximum sunspot number of 90. Given the date of solar minimum and the predicted maximum intensity, solar maximum is now expected to occur in May 2013. Note, this is not a unanimous decision, but a supermajority of the panel did agree.”

But according to Pesnell -- given the lack of solar activity in February 2013 -- a maximum in May now seems unlikely. “We may be seeing what happens when you predict a single amplitude and the Sun responds with a double peak,” he said.  -- Thanks to NASA, Dr Tony Phillips and Science@NASA for the information



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