RICHLAND, Wash. -- Atmospheric scientists trying to pin down how clouds curb the amount of sunlight available to warm the earth have found that it depends on the wavelength of sunlight being measured. This unexpected result will help researchers improve how they portray clouds in climate models.
Additionally, the researchers found that sunlight scattered by clouds the reason why beachgoers can get sunburned on overcast days is an important component of cloud contributions to the earth's energy balance. Capturing such contributions will increase the accuracy of climate models, the team from the Department of Energy's Pacific Northwest National Laboratory reported in Geophysical Research Letters earlier this month.
"The amount of the sun's energy that reaches the earth's surface is the main driver of the earth's temperature. Clouds are one of the least understood aspects of climate change. They can block the sun, but light can also bounce off one cloud into another cloud's shadow and increase the solar energy hitting earth," said PNNL atmospheric scientist Evgueni Kassianov.
Clouds both cool down and warm up the earth's surface. They cool the earth by reflecting some sunlight up into outer space, and they warm it by bouncing some sunlight down to the surface. Overall, most clouds have a net cooling effect, but atmospheric scientists need to accurately measure when they cool and warm to produce better climate models that incorporate clouds faithfully.
But it's a hard number to get. Fair-weather clouds are big puffy white objects that bounce a lot of light around. They can make the sky around them look brighter when they're there, but they float about and reform constantly. Cloud droplets and aerosol particles in the sky tiny bits of dirt and water in the air that cause haziness scatter light in three dimensions, even into cloud shadows.
To determine the net cloud effect, researchers
|Contact: Mary Beckman|
DOE/Pacific Northwest National Laboratory