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The polar climate affects the strength of trade winds in the tropics

Long-distance connection: the polar climate affects the strength of trade winds in the tropics

The blue ice covering Lake Fryxell in the Trans-Antarctic Mountains comes from melted glacier water. Credit: Joe Mastroianni, National Science Foundation

The impact of sea surface temperature changes in the tropical Pacific on global climate has long been recognized. For example, the occasional warming of the tropical Pacific Ocean during the events in El Niño led to the melting of sea ice in distant parts of the Southern Ocean through its effect on global atmospheric circulation. A new study published this week in the journal Scientific progress from an international team, shows that there is a reverse path.

Using a hierarchy of climate model simulations, the authors demonstrate the physical pathways by which polar climate variations can affect trade winds in the tropics.

“Climate signals can travel from the polar regions to the tropics, either through the atmosphere or across the ocean,”

; said Malte Stucker, co-author and assistant professor of oceanography and the International Center for Pacific Studies at the University of Hawaii in Manoa. “Our simulations of climate models are designed to examine the relative role of these roads and whether their significance differs in disturbances originating at the North or South Pole.”

The authors found that in the most complex simulations of models, which include realistic images of the ocean, atmosphere, land and sea ice, abnormal cooling in both hemispheres leads to the strengthening of tropical trade winds.

Lead author Sarah Kang of the National Institute of Science and Technology in Ulsan, South Korea, explained the reasons for these experiments: “One of the biggest sources of uncertainty in the current generation of climate models is the bias in the representation of clouds over the cold Southern Ocean. We wanted to study what effect the excessive radiation of solar clouds from these clouds in outer space could have on the global climate. In addition, large aerosol emissions in the late 20th century due to industrial activity in the Northern Hemisphere from North America, Europe, and Asia led to a slight temporary reduction in global warming due to increased greenhouse gas emissions. “

According to the authors, both effects could potentially explain why Pacific trade winds have been abnormally strong in recent decades.

“If communication between the poles and the tropics were to take place only through the atmosphere, we would see a very clear response in the tropics, depending on whether the abnormal cooling originated in the Arctic or Antarctic,” Stucker added. “This is because the Intertropical Convergence Zone – the largest rainforest on Earth – is located north of the equator. It effectively blocks communication from the Arctic to the equator through the atmosphere.”

Contrasting experiments with and without a realistic representation of the ocean, the authors show that the increased rise of cold groundwater in the eastern tropical Pacific Ocean is able to communicate the cooling of the Arctic to the tropics and thus strengthen trade winds.

Important of the results is that the reduction of uncertainty in the simulated extratropical climate can also lead to improved climate simulation in the tropics. The model hierarchy developed by the authors can be used for further study of the two-way interactions between the tropics and the polar regions both for future climate forecasts and for interpreting reconstructions of climatic conditions in the geological past.

The accuracy of the El Nino simulation is important for predicting the future climate

More info:
“Walker’s Circulation Response to Extratropical Radiation Coercion” Scientific progress (2020). DOI: 10.1126 / sciadv.abd3021

Provided by the University of Hawaii at Manoa

Quote: Long-distance connection: The polar climate affects the strength of trade winds in the tropics (2020, November 20), extracted on November 21, 2020 from https://phys.org/news/2020-11-distance-polar- climate-affects-strength.html

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