HUNTSVILLE, Ala., March 2 (UPI) -- Solar physicists say despite a recent flare-up of activity on the sun, the current phase in its 11-year activity cycle isn't measuring up to what was forecast.
"This cycle continues to fall below expectations," David Hathaway of NASA's Marshall Space Flight Center in Huntsville, Ala., says. "And those expectations were pretty low two years ago."
The number of sunspots is one indicator of solar activity, and scientists say they expect this will be the weakest sunspot cycle in 200 years, ScienceNew.org reported Wednesday.
For a 780-day period ending in March 2010, not a single sunspot was observed. During a more typical solar minimum, researchers say, the sun is spot-free for about 300 days.
"We are off to a good start for a below-average cycle peaking in late 2013 or early 2014," Dean Pesnell of NASA's Goddard Space Flight Center in Greenbelt, Md., says.
Solar physicists say they think a flow of ionized gas, or plasma, known as the meridional flow under the sun's surface that seems to control the strength of the solar cycle, is responsible.
The speed of the flow seems to be a critical factor, they say. A fast flow during the first half of a solar cycle, followed by a slower flow during the second half, creates a weak polar magnetic field that generates an unusually weak and prolonged solar minimum like the current one, says Dibyendu Nandy of the Indian Institute of Science Education and Research.
A weaker solar cycle is accompanied by a slightly dimmer sun, which changes the average temperature on Earth.
The exact role the flow plays in the solar cycle remains a matter of debate but research "demonstrates how the inner working of the sun, and variations in the plasma flow deep within our parent star can control its magnetic and energetic output, which in turn, determines the environment in space and affects climate on Earth," Nandy says.
