U. WASHINGTON (US) — A large wave structure in the atmosphere has been bringing steadily warmer temperatures to West Antarctica during the winter and spring for at least 30 years.
New research shows that rising sea surface temperatures in the tropical Pacific Ocean along the equator and near the International Date Line are driving the atmospheric circulation, called a Rossby wave train, causing some of the largest shifts in Antarctic climate in recent decades.
Antarctica is somewhat isolated by the vast Southern Ocean, but the results “show that it is still affected by climate changes elsewhere on the planet,” says Eric Steig, professor of earth and space science at the University of Washington.
Scientists used surface and satellite temperature observations to show a strong statistical connection between warmer temperatures in Antarctica, largely brought by westerly winds associated with high pressure over the Amundsen Sea adjacent to West Antarctica, and sea surface temperatures in the central tropical Pacific Ocean.
A strong relationship was found between central Pacific sea-surface readings and Antarctic temperatures during winter months, June through August. Though not as pronounced, the effect also appeared in the spring months of September through November.
The study is reported in the journal Nature Geoscience.
The observed circulation changes are in the form of a series of high- and low-pressure cells that follow an arcing path from the tropical Pacific to West Antarctica, characteristic of a textbook Rossby wave train pattern, says postdoctoral researcher and lead author Qinghua Ding, and the same pattern is consistently produced in climate models, at least during winter.
Using observed changes in tropical sea surface temperatures, the researchers found they could account for half to all of the observed winter temperature changes in West Antarctica, depending on which observations are used for comparison.
“This is distinct from El Niño,” Steig says. That climate phenomenon, which affects weather patterns worldwide, primarily influences sea-surface temperatures farther east in the Pacific, nearer to South America. It can be, but isn’t always, associated with strong warming in the central Pacific.
The influence of Rossby waves on West Antarctic climate is not a new idea, but this is the first time such waves have been shown to be associated with long-term changes in Antarctic temperature.
The findings also could have implications for understanding the causes behind the thinning of the West Antarctic Ice Sheet, which contains about 10 percent of all the ice in Antarctica.
Westerly winds created by the high pressure over the Amundsen Sea pushes cold water away from the edge of the ice sheet and out into the open ocean. It is then replaced by warmer water from deeper in the ocean, which is melting the seaward edge of the ice sheet from below.
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