Fewer sunspots will erupt on the sun's surface during the next decade, indicating an unexpected decrease in the activity of magnetic fields that churn the sun's hot gases, Yale and NASA astronomers predict. The milder "space weather" -- marked by a decrease in magnetic storms, cosmic rays and ionspheric disturbances -- could bring cooler temperatures on earth, fewer power blackouts and less interference with radio waves.
The optimistic prediction, which contradicts that of many other scientists, was reported on Jan. 14 at a meeting of the American Astronomical Society in Toronto, Canada, by Kenneth Schatten of Goddard Space Flight Center-NASA in Greenbelt, Maryland. He and Sabatino Sofia, chair of Yale's astronomy department, inferred the magnitude of magnetic fields just below the sun's surface from observations with solar telescopes in Stanford and Big Bear, California.
The researchers noted that the sun's magnetic activity, which waxes and wanes in cycles lasting about 11 years, is as notoriously unpredictable as the weather. "During the last 50 years, the sun has displayed more activity than it has since Galileo first observed sunspots in the early 1600s," says Professor Sofia, who is also associate director of Yale's Center for Solar and Space Research. "Thus, if the next solar cycle shows a downward trend, it could reverse the general rise in activity which has occurred during the past 400 years."
Variations in solar activity have been linked to long-term climate changes on earth, such as the global phenomenon known as the "Little Ice Age" in the 1600s, which was triggered by a century of little solar activity. The relatively abrupt cooling froze the Thames River and caused glaciers around the world to advance. At the other extreme, increased solar activity during the 11th and 12th centuries may have triggered global warming that enabled the Vikings to inhabit Greenland, which they were forced to abandon when solar activity waned, Mr. Schatten says.
If the researchers' prediction for the coming decade proves accurate, the milder space weather could help moderate global warming expected from the greenhouse effect. It also would be good news for NASA, the Air Force and other organizations whose high- tech equipment is often affected by solar storms, Professor Sofia says. For example, the enhanced "drag" caused by a thickening in the earth's upper atmosphere during solar storms can make satellites fall from orbit prematurely. The shortened life of the Skylab satellite in the late 1970s was due to the exceptionally high level of solar activity at that time.
Furthermore, enhanced solar cosmic rays can sometimes cause "glitches" in the sophisticated electronic systems of satellites, while large solar storms have been known to cause widespread power blackouts, especially in northern latitudes, when power surges blow out transformers.
Not everyone agrees with the Schatten-Sofia model for predicting solar activity, which is based on the physics of how magnetic fields are generated within the sun by a "dynamo" process, similar to the way an automobile alternator generates electrical voltages. Their Solar Dynamo Amplitude index -- which they call the SODA index because it provides a prediction of the amount of magnetic flux, or "fizz," below the sun's surface -- indicates that the next solar cycle will peak in the year 2000.
Many statisticians are predicting a continued increase in solar activity, based on recent patterns of fluctuations, says Mr. Schatten, who explained that solar physicists divide cycles into odd and even pairs. For most cycles -- and for all during this century -- solar activity during the odd cycle of a pair exceeded that during the previous even-numbered cycle. Since the current, even-numbered cycle was the second largest in recorded history, the next cycle would be expected to be larger still. Yet, the Schatten-Sofia model predicts a significant downturn.
"Are solar cycles random, or do they follow rules and behave predictably, in the manner that planets orbit the sun? Put simply, will our prediction technique beat the statistical rules, or will the statisticians win? Stay tuned," says Professor Sofia.