RICHLAND, Wash. -- Pollution is warming the atmosphere through summer thunderstorm clouds, according to a computational study published May 10 in Geophysical Research Letters. How much the warming effect of these clouds offsets the cooling that other clouds provide is not yet clear. To find out, researchers need to incorporate this new-found warming into global climate models.
Pollution strengthens thunderstorm clouds, causing their anvil-shaped tops to spread out high in the atmosphere and capture heat -- especially at night, said lead author and climate researcher Jiwen Fan of the Department of Energy's Pacific Northwest National Laboratory.
"Global climate models don't see this effect because thunderstorm clouds simulated in those models do not include enough detail," said Fan. "The large amount of heat trapped by the pollution-enhanced clouds could potentially impact regional circulation and modify weather systems."
Clouds are one of the most poorly understood components of Earth's climate system. Called deep convective clouds, thunderstorm clouds reflect a lot of the sun's energy back into space, trap heat that rises from the surface, and return evaporated water back to the surface as rain, making them an important part of the climate cycle.
To more realistically model clouds on a small scale, such as in this study, researchers use the physics of temperature, water, gases and aerosols -- tiny particles in the air such as pollution, salt or dust on which cloud droplets form.
In large-scale models that look at regions or the entire globe, researchers substitute a stand-in called a parameterization to account for deep convective clouds. The size of the grid in global models can be a hundred times bigger than an actual thunderhead, making a substitute necessary.
However, thunderheads are complicated, dynamic clouds. Coming up with an accurate parameterization is important but has been difficult du
|Contact: Mary Beckman|
DOE/Pacific Northwest National Laboratory