MODEL HELPS SCIENTISTS HOME IN ON TROPICAL CLIMATE CONTROLS

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MODEL HELPS SCIENTISTS HOME IN ON TROPICAL CLIMATE CONTROLS
21 May 2003 - University of Wisconsin-Madison

It has long been known that tropical climate, by redistributing vast amounts of solar energy through welling hot air and the formation of towering cumulous clouds, influences weather in other parts of the world.

It remains unclear, however, how much the tropics can be affected by higher latitudes.

Now, with the help of a sophisticated computer model, scientists at the University of Wisconsin-Madison have shown that vast atmospheric "bridges" and oceanic "tunnels," created by overturning air and water, link the high latitudes to the tropics and can warm ocean temperature near the equator.

The finding, reported in the May 13 issue of the journal Geophysical Research Letters, has implications for better understanding global and regional climate change, and is the first to identify high-latitude phenomena that significantly influence climate in the equatorial regions of the world.

The prevailing wisdom, according to Zhengyu Liu, lead author of the paper and director of UW-Madison's Center for Climatic Research, was that climate and weather phenomena at higher latitudes tended to be static, with no far-reaching influence.

"That was the conventional thinking," he says. "But our model shows that these phenomena are equally weighted, that climate and weather at higher latitudes have as much of an influence on the tropics as tropical weather and climate influence the higher latitudes. Both are very important."

The discovery reveals a hidden climate mechanism that may be of critical importance to studies of past and future global and regional climate change, says Liu.

According to the scenario depicted by the modeling experiments conducted by Liu and colleague Haijun Yang, the heat carried via the atmospheric bridges from the tropics to higher latitudes is reduced as a result of warming climate in the higher latitudes. At the same time, warm extratropical water is funneled into the subsurface oceanic tunnels and is carried to the equator where it upwells and warms the tropical ocean.

The study suggests that even a 2-degree Celsius warming of the ocean in regions beyond the tropics can raise ocean surface and subsurface temperatures in the tropics by as much as 1 degree Celsius as less warm air flows out of the tropics and warm, extratropical water is channeled toward the equator by the oceanic tunnels depicted in the study.

"That is a significant change" in temperature, says Liu. "It is fundamentally important."

The new study, says Liu, provides a missing piece of the climate puzzle. It will enable scientists to gain more insight into climate and climate change as an unknown mechanism is revealed and added to the mix of variables that researchers must grasp as they wrestle with the hugely complex problem of understanding and forecasting climate change.

"The magnitude of this influence and the relative contributions of the atmospheric bridge and oceanic tunnel have remained uncertain," Liu says. "But we have found that the extratropics exert a strong control on tropical climate. This is our first estimate of the extratropical influence on the tropics."

The Center for Climatic Research at the University of Wisconsin-Madison is a leading center of research into world climate. It is a part of the UW-Madison Gaylord Nelson Institute for Environmental Studies.

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About: University of Wisconsin-Madison
In achievement and prestige, the University of Wisconsin-Madison has long been recognized as one of America’s great universities. A public, land-grant institution, UW-Madison offers a complete spectrum of liberal arts studies, professional programs and student activities. Many of its programs are hailed as world leaders in instruction, research and public service.

The university traces its roots to a clause in the Wisconsin Constitution, which decreed that the state should have a prominent public university. In 1848, Nelson Dewey, Wisconsin’s first governor, signed the act that formally created the university, and its first class, with 17 students, met in a Madison school building on February 5, 1849.

From those humble beginnings, the university has grown into a large, diverse community, with about 40,000 students enrolled each year. These students represent every state in the nation, as well as countries from around the globe, making for a truly international population.

UW-Madison is the oldest and largest campus in the University of Wisconsin System, a statewide network of 13 comprehensive universities, 13 freshman-sophomore transfer colleges and an extension service. One of two doctorate-granting universities in the system, UW-Madison’s specific mission is to provide "a learning environment in which faculty, staff and students can discover, examine critically, preserve and transmit the knowledge, wisdom and values that will help insure the survival of this and future generations and improve the quality of life for all."

The university achieves these ends through innovative programs of research, teaching and public service. Throughout its history, UW-Madison has sought to bring the power of learning into the daily lives of its students through innovations such as residential learning communities and service-learning opportunities. Students also participate freely in research, which has led to life-improving inventions from more fuel-efficient engines to cutting-edge genetic therapies.

Students, faculty and staff are motivated by a tradition known as the "Wisconsin Idea," described by UW President Charles Van Hise in 1904 as the compelling need to carry "the beneficent influence of the university ... to every home in the state." The Wisconsin Idea permeates the university’s work and helps forge close working relationships among university faculty and students and the state’s industries and government.

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