August 28, 2009

The Impact Of Sun Spots On Earth’s Climate

Researchers from NCAR have created the first-ever model to simulate the impact of the sun's radiation fluctuations on the earth's climate.

Scientists have long known that the sun does not radiate evenly. The best known example of radiation fluctuations is the famous 11-year cycle of sun spots. But experts have previously been unable to create a model that would depict how uneven radiation would impact the earth's climate.

"Small changes in the sun's output over the 11-year solar cycle have long been known to have impacts on the global climate system," said Julie Arblaster, from the Centre for Australian Weather and Climate Research, a co-author of the study.

Writing in the journal Science, researchers from the US and Germany discussed their new model, which shows how solar radiation interacts with the atmosphere and ocean patterns.

Lead author Gerald Meehl of the National Center for Atmospheric Research (NCAR) and colleagues calculated how small variations in radiation bring about a comparatively significant change in the System "Atmosphere-Ocean".

"Taking into consideration the complete radiation spectrum of the sun, the radiation intensity within one sun spot cycle varies by just 0.1 per cent. Complex interplay mechanisms in the stratosphere and the troposphere, however, create measurable changes in the water temperature of the Pacific and in precipitation," said co-author Katja Matthes of the GFZ German Research Centre for Geosciences.

Scientists relied on weather data over the course of a century to create their model, which shows that even small variations could intensify wind and rainfall.

"Here we reconcile for the first time the mechanisms by which these small variations get amplified, resulting in cooler sea surface temperatures in the tropical Pacific and enhancing off-equatorial rainfall."

As a part of the first process, increased solar radiation leads to more ozone and higher temperatures in the stratosphere, researchers noted.

"The ultraviolet radiation share varies much more strongly than the other shares in the spectrum, i.e. by five to eight per cent, and that forms more ozone," said Matthes.

The second process works the opposite way, by allowing increased solar radiation to cause more evaporation in cloud free regions.

"It is this positive back coupling that strengthens the process," said Matthes.


On the Net: