When low-level clouds dissipate
When the oceans warm, water evaporates and cloud cover increases. This is the well known science behind cloud formation. A new study begs to differ. Of the three major kinds—low, mid and high—low-level clouds are believed to form as oceans warm and act as a blanket between the solar radiations and the earth. Thus they act as buffers, preventing further heating of the oceans.
Robert Burgman, an atmospheric scientist from the Miami University, USA, found evidence to the contrary. With an increase in sea surface temperatures, a certain type of low-level clouds (stratiform) are decreasing in number. This decrease could, in turn, increase the warming of the oceans.
Burgman tracked the low level clouds over the Northeast Pacific Ocean. He explained the atmospheric mechanism which leads to the dissipation of these low-level, relatively dry clouds: water droplets remain suspended (as clouds) above the surface of the sea but cannot escape further upwards as they are arrested by the layer of warmer air aloft.
Vicious cycle
As the sea warms further, more of such clouds should be formed. But an increase in temperature over the surface of the sea weakens the atmospheric circulation in the Pacific Ocean.
This causes the upper layer of warm air to thin down which, in turn, allows the low-level clouds to dissipate, explained the atmospheric scientist.
“This is somewhat of a vicious cycle potentially exacerbating global warming,” said Amy Clement, meteorologist at Miami University, who was part of the study.
The team arrived at their conclusions using observational data collected over the last 50 years and complex climate models for the northeast Pacific Ocean.
One set of data consisted of visual observations gathered from ships over the last 50 years, and the other was based on data collected from weather satellites.
However, only one climate model of the several that the researchers employed to arrive at their conclusions, could replicate the observations.
“It is not surprising that only one climate model was able to reproduce the observed features over NE Pacific,” said M Rajeevan, scientist at the National Atmospheric Research Laboratory, Tirupati. “It is an important development but we are yet to see how this will affect the Indian Ocean. In general, the clouds-global warming relationship over the Indian Ocean is different from other oceanic basins,” he added.
Rajeevan’s study published in Current Science in 2000 showed that though cloud cover over Bay of Bengal decreased with increase of sea surface temperatures after mid 1980s, cloud cover over parts of the Indian Ocean around the equator kept increasing.
While Rajeevan and his team in 2,000 used data of low and total cloud cover collected from observations by Voluntary Observing Ships which report as per the World Meteorological Organisation code, the Miami team used multiple data sources.
