London, September 29 : A new research has suggested that increased solar activity - associated with sunspots - means more ultraviolet radiation reaching the Earth's upper atmosphere, resulting in a decrease in hurricane intensity.
According to a report in Nature News, James Elsner, a climatologist at Florida State University in Tallahassee, has analyzed hurricane data going back more than a century.
He said that he has identified a 10- to 12-year cycle in hurricane records that corresponds to the solar cycle, in which the Sun's magnetic activity rises and falls.
Solar activity varies on a roughly 11-year cycle, in which its magnetic activity waxes and wanes. The idea is that increased solar activity - associated with sunspots - means more ultraviolet radiation reaching the Earth's upper atmosphere. That warms the airs aloft and decreases the temperature differential between high and low elevations that otherwise would fuel hurricanes.
"Our results indicate that there is an effect in the intensity of storms due to the higher temperatures aloft," said Elsner.
He said that the statistical analysis suggests a 10 percent decrease in hurricane intensity for every 100 sunspots. At the peak of its cycle, the Sun might exhibit around 250 sunspots.
Establishing such a relationship would be enormously valuable, providing researchers, meteorologists and insurance companies with another tool for predicting storms and assessing financial liabilities.
For the new study, Elsner and a post-doctoral student, Thomas Jagger, used more than a century of records on hurricanes that reached land in the United States as a proxy for records on hurricane intensity.
The assumption is that the effect on overall hurricane intensity would make itself evident as more or fewer hurricane-strength storms made land.
According to Elsner, the solar-cycle pattern emerged after his team had already taken into account major factors such as sea-surface temperatures.
The team also found a correlation when comparing sunspot records with daily intensity values for storms dating back to 1944, using "best-track" records from the National Hurricane Center.
"It gives us some faith that we are probably on to something here," Elsner said.