Cold air, why does it rise and fall in tropical areas?
Conventional knowledge states that hot air rises as cold air sinks. But a University of California study found that in the tropical atmosphere the cold air rises due to a neglected effect: the lightness of water vapor. This effect helps stabilize tropical climates and mitigate some of the impacts of a hot climate.
The study, published today in the journal Science Advances, is among the first to show the profound implications of water vapor buoyancy on Earth’s climate and energy balance.
Cold air rises in tropical areas
“Water vapor is known to be an important greenhouse gas that warms the planet,” said the senior author From Yang, assistant professor of atmospheric sciences at Davis University. “On the other hand, water vapor has a buoyancy effect which helps release heat from the atmosphere into space and reduces the degree of heating. Without this lightness of water vapor, global warming would be even worse. “
Humid air is lighter than dry air under the same temperature and pressure conditions. This is called the effect of buoyancy of the vapor. This study found that this effect allows cold, humid air to rise, forming clouds and thunderstorms in the tropics of the Earth. Meanwhile, hot, dry air sinks into clear skies. Earth’s atmosphere then emits more energy into space than it would without the buoyancy of vapor.
“Now that we understand how lightness of water regulates tropical climate, we plan to investigate whether global climate models represent exactly this effect,” said the study’s lead author. Seth Seidelan undergraduate research student at UC Davis.