New research suggests the expansion of the tropics and air circulations known as the Hadley cells are pushing high altitude clouds toward the poles. Photo by NASA/Goddard
NEW YORK, May 5 (UPI) -- A survey of 30 years worth of satellite data suggests high altitude clouds are shifting closer to the poles. Now, researchers have a good idea why.
High altitude clouds are those found between three-and-a-half and six miles high. Some scientists have suggested the shifting jet streams are pulling middle-latitude cloud systems toward the poles.
Scientists at NASA's Goddard Institute for Space Studies designed a model to analyze the correlation between cloud positions and climatic factors. Their simulations suggest the expansion of the tropics and the circulation of air known as the Hadley cell are the primary drivers of the polar drift.
"What we find, and other people have found it as well, is that the sinking branch of the Hadley cell, as the climate warms, tends to be moving poleward," George Tselioudis, a climate scientist at Goddard and Columbia University, said in a news release. "It's like you're making the tropical region bigger."
Tselioudis and his colleagues published their findings this week in the journal Geophysical Research Letters.
The Hadley cell circulation begins with rising air in the tropics, and as it pushes northward and southward away from the equators, it sinks back towards Earth's surface. As the tropics grow, these currents are pushing high-altitude clouds toward the North and South Pole.
Cloud cover and cloud formation patterns play an important role in dictating the planet's climate, as their presence reflect a significant amount of sunlight, enduing them with a cooling presence. In their absence, land and sea absorb greater amounts of the sun's energy.
The influence of global warming on cloud patterns -- and vice versa -- is an important part of understanding and predicting climate change.
"If current behavior is not well simulated, then confidence in predicted future behavior will be lower," added Lazaros Oreopoulos, a cloud scientist at Goddard. "I anticipate this study to be looked at carefully and affect thinking on these matters."