Drought might be the result of sunspots

Meteorologists point to past dry spells that triggered heat waves

August 07, 1999|By Douglas Birch | Douglas Birch,SUN STAFF

The heat and drought searing this region might have been spawned by violent storms sweeping the sun, says Pennsylvania's climatologist.

In weather records for Northeast cities, Paul Knight of Pennsylvania State University found that the hottest, driest periods tend to occur during the most intense periods of sunspot activity.

Sunspots are storms of atomic particles and electromagnetic energy that erupt over the sun's surface. They vary over time, reaching a peak every 11 years during what is called the "solar maximum."

Knight says that about a third of the hottest days on record in this century occurred during a solar maximum year. This year marked a solar maximum. So did the drought years of 1988-1989, a time of record heat.

Heat waves are typically triggered by dry conditions. "Drought and heat are cousins," he says. "And it's really the drought that produces the heat."

For centuries, scientists have suspected that sunspots affected weather patterns. Astronomers noticed that the sun's surface was unusually quiet between 1645 and 1715, when global temperatures fell by about a half-degree.

But winnowing causes from mere coincidences is hard to do with something as complicated as the climate.

Scientists found that the most intense solar storms increased the amount of solar energy reaching Earth by just one-tenth of 1 percent. It seemed to be too feeble a change to alter weather patterns.

Over the past two decades, new evidence has changed this view, says Drew T. Shindell, a research scientist at the Goddard Institute for Space Studies in New York City.

Satellite instruments, he says, showed that the most intense solar storms can cause a 10 percent rise in the amount of one type of sunlight -- ultraviolet radiation -- that strikes the high-altitude ozone layer.

"The bulk of the influence from solar variability seems to directly affect the upper atmosphere," he says. "People usually have ignored this because they think it's too high up, it can't have any effect on climate."

But evidence suggests that this periodic boost of energy changes the pattern of high-altitude winds, which in turn stir the thicker soup of gases swirling closer to the planet's surface.

Scientists have linked higher temperatures over the north Pacific to intense sunspots. They have also shown that storms over the North Atlantic move away from the North Pole during solar maximums.

English scientists reported in the journal Nature two months ago that the sun's magnetic field has more than doubled in strength in the past century, causing the sun to burn brighter.

"As much as half of the global warming that's occurred in the last hundred years is due to increased sunspot activity," estimates Brian A. Tinsley, a physicist at the University of Texas at Dallas.

"There is a growing awareness in recent years that there is likely a real relationship between solar activity and climate," says Stephen P. Maran, spokesman for the American Astronomical Society. But blaming solar storms for local weather conditions, such as this year's mid-Atlantic drought, is another matter.

"There have been many past results where meteorologists and other scientists have found correlations between rainfall and drought in specific geographic areas, notably in the United States," he says.

"Those results in every case go away after you have one or two more sunspot cycles, and you see that it was a random correlation."

Knight can't explain how Northeast droughts might be connected to sunspots. But, he says, the two occur together "much more frequently than would be expected at random."

The Pennsylvania meteorologist, meanwhile, says that while the current drought is already one of the worst of the 20th century, "it can get much worse. And it can last for years."

Three times since 1900, Knight says, the region has suffered through droughts that spanned about a decade, with occasional sprinkles of relief. Only in the past 30 years, he says, have arid periods been fleeting, stretching over no more than about 18 months.

"Look back into the 1960s, pretty much 1961 to 1969 was dry," Knight says. "There were lots of signs telling people how to conserve water. Desalinization of sea water became a big issue. In the '60s, we were talking about the reservoir levels in many urban areas down below 50 percent."

The Dust Bowl drought lasted almost a decade in this region. It peaked in Maryland in February 1931, National Weather Service data show, when water concentrations in the soil were half again as low as they are now.

If the current drought follows the recent pattern, it shouldn't last more than six more months. But there is no guarantee; there is reason to fear that it is settling in for the long haul.

"Here is the scary part about this," Knight says. The depths of a drought typically occur from October to March, normally the driest months. But this summer hasn't brought the downpours typical of the season.

"We haven't had much rainfall, and we're heading into the dry part of the year," Knight says. "It's like we've just emptied our savings and the big bills are coming."

The Chesapeake region has long been subject to severe droughts. One of the worst occurred starting about 1600, around the time of the settlement of Jamestown, says Grace S. Brush, professor at Johns Hopkins University.

An analysis of pollen and seeds in bay sediments show that drought lasted more than a decade and scorched the landscape.

"The pollen record doesn't show anything in the last 100 years like what we saw then," she says.

Pub Date: 8/07/99

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