The cycle that causes the surface of the sun to spot and flare every 11 years was linked for the first time yesterday to cross-currents of hot gas that migrate from the sun's poles to its equator every 22 years.
"This doesn't solve the riddle of the cycle but it's a very important clue to a better understanding of the cycle," said Dr. Robert Howard of California's Hale Observatories, where the observations were made.
"This doesn't mean what we can ever do anything about the cycle, but it would be comforting to know what its limits are in terms of its impacts on the Earth," he said.
Sunspots and solar flares trigger magnetic storms that disrupt radio communications and interfere with power transmissions on Earth. Some scientists have linked sunspot activity with droughts and climate changes, such as the Little Ice Age in the 17th century, when sunspots almost disappeared from the surface of the sun.
"There was a flare in the 1860s that was so bright it was seen with the naked eye." Howard said yesterday at the Carnegie Institution, which together with the California Institute of Technology sponsors the work at Hale Obervatories. "The resulting magnetic storm was so strong it was even noticeable in the crude instruments available then, and which surely would have caused a major disruption of satellite communications today."
In an experiment that took 12 years, Howard found that sunspots break out in the boundary regions between a pair of east-west currents that migrate north and south to the sun's equator.
He said there are always two sets of currents migrating in each hemisphere, one starting a new sunspot cycle of 11 years and the other ending an old one.
"We already see the evidence of the next solar cycle at high latitudes on the solar disc," Howard said. "This is the first time anybody has ever had any indication of any sort of a precursor of the next cycle."
Howard, who made the observations with Dr. Barry LaBonte using the 150-foot-tall solar telescope at Mount Wilson Observatory, said that each set of currents has a fast one and a slow one. The fast current rotates about eight miles an hour faster than the rest of the sun, and the slow current about eight miles an hour slower than the gas that makes up the solar disc.
Every 11 years a new fast current appears at each pole and is quickly followed by a slow current. In 11 years, the currents move about halfway to the solar equator and sunspots break out between the boundaries of the currents.
"This is where we see the period that's called the solar maximum," Howard said. "This is where we see the maximum number of sunspots in any cycle, and whatever flaring that goes on in sunspot groups."
It takes 22 years for each set of currents to reach the equator, at which time sunspots disappear from the boundaries between the currents.
"The spots just peter out above and below the equator," Howard said "We haven't the foggiest notion why, except that it marks the end of another solar cycle."