With the sun at its lowest activity level in nearly 100 years, scientists are taking advantage of its quiet state to ferret out some of the more subtle — and occasionally insidious — ways the sun impacts Earth's climate and atmosphere.
Solar flares and other geomagnetic events on the sun vary in frequency over an 11-year cycle. Now at an unusually low "minimum" in that cycle, the sun is expected to peak in activity in 2013.
"If you thought that the globe was going to warm up because there was more solar activity, you might perhaps expect it to get warmer everywhere, and this is not the case," said Joanna Haigh, an atmospheric physicist with Imperial College in London.
Haigh and her colleagues, who have been studying the sun in its relatively dormant state, have found an apparent connection between solar activity and regions of warming around Earth's midsection.
She is quick to point out that the phenomenon cannot account for the rise in global temperatures seen over the past 50 years. "The point is there is a significant effect of the sun on local climate, not global," said Haigh.
In an upcoming paper, Haigh's team provides evidence that when the sun is more active, Earth's jet streams weaken and shift toward the poles, taking with them storm tracks and weather systems that carry heat. The result is a subtle warming around Earth's mid-latitudes.
"We're beginning to understand how these processes take place," Haigh said.
The sun's quiescence also has enabled researchers to figure out that ozone-depleting nitric oxide can pass from the upper atmosphere to the stratosphere below without the geomagnetic effects of solar storms, which were once given credit for the phenomenon.
Scott Bailey, an associate professor at Virginia Polytechnic Institute's Center for Space Science and Engineering, and colleagues found that twice during the sun's quiet period, significant amounts of nitric oxide — enough to consume 30 percent more ozone than expected — have been transported to the lower atmosphere.
Rather than solar activity, the researchers credit atmospheric winds and temperature shifts.
"This is not an effect that will change the amount of ozone in some significant way that would impact life," Bailey said at the American Geophysical Union conference in Toronto this week. "It's not going to cause large increases in skin cancer or other things like if you were to totally remove all the ozone, but it is enough to change some properties of the stratosphere."
Nitric oxide is produced in the upper atmosphere along with beautiful auroras when charged particles from the sun interact with Earth's magnetic field. Most of the molecules are quickly destroyed by sunlight, but due to long, dark winters at Earth's poles, supplies of nitric oxide can hang around there for as long as 20 years.
Researchers previously believed the molecules would only reach the lower atmosphere during solar storms. That turned out not to be the case.
"It's very useful to have a long period of quiet in order to understand these long-period changes in the atmosphere that might take a year or two to develop," said Christopher Russell, a professor of geophysics and space Physics at the University of California, Los Angeles. "We need the sun to shut up for a few years and allow us to probe that."