Despite a recent flare, solar physicists project low activity for up to a decade
A powerful explosion that erupted on the solar surface on February 14 was the most powerful flare in more than four years, and heralds an approaching peak in the sun’s 11-year activity cycle. But as the sun pulls out of an exceptionally quiet period of low activity, researchers predict the coming solar maximum won’t be very exciting either.
“This cycle continues to fall below expectations. And those expectations were pretty low two years ago,” says David Hathaway of NASA’s Marshall Space Flight Center in Huntsville, Ala.
The number of sunspots — dark, highly magnetized regions on the solar surface — is one indicator of solar activity, and scientists now predict this will be the weakest sunspot cycle in 200 years. “We are off to a good start for a below-average cycle peaking in late 2013 or early 2014,” says Dean Pesnell of NASA’s Goddard Space Flight Center in Greenbelt, Md.
Understanding how present activity affects future cycles is important to gauging both the sun’s influence on climate and its likelihood of producing powerful and destructive solar storms.
Solar physicists say they are homing in on the complex internal interactions that could explain why the sun has been hibernating for more than four years now and may not fully awaken for another decade. Hathaway and other researchers say they’re now convinced that a flow of ionized gas, or plasma, known as the meridional flow controls the strength of the solar cycle (SN: 4/10/11, p. 8
).On either side of the equator, the flow moves like a conveyor belt that stretches just beneath the solar surface from the equator to the two poles and then dives into the sun’s interior, flowing from the poles back to the equator to complete the loop.