The impact of ocean surface temperature variations in the tropical Pacific on the global climate has long been recognized. For example, during the El Niño events, the episodic warming of the tropical Pacific Ocean causes melting of sea ice in far-reaching parts of the southern ocean through its impact on global atmospheric circulation. A new study published this week in the journal Scientific progress demonstrated by an international team that the opposite path also exists.
Using a hierarchy of climate model simulations, the authors demonstrate the physical paths through which polar climate variations can affect trade winds in the tropics.
“Climate signals can spread from the polar regions to the tropics either via the atmosphere or the ocean,”
The authors found that in the most complex model simulations, which include realistic representations of the ocean, atmosphere, land, and sea ice, irregular cooling on both hemispheres leads to a strengthening of the tropical trade winds.
Lead author Sarah Kang of the Ulsan National Institute of Science and Technology in South Korea explained the reasoning behind these experiments: “One of the biggest sources of uncertainty in the current generation of climate models is bias in the representation of clouds over the cold southern ocean. what effect too much solar radiation reflection from these clouds into outer space can have on the global climate.In addition, large emissions of aerosols in the late 20th century due to industrial activity in the northern hemisphere from North America, Europe and Asia resulted in a slight, temporary reduction in global warming due to rising greenhouse gas emissions. “
According to the authors’ results, both of these effects could potentially explain why trade winds in the Pacific were abnormally strong in recent decades.
“If the communication between the poles and the tropics were to take place only via the atmosphere, we would see a fairly clear response in the tropics depending on whether an irregular cooling occurs from the Arctic or the Antarctic,” Stuecker added. “This is because the intertropical convergence zone – the largest rainbow on Earth – lies north of the equator. It effectively blocks communication from the Arctic to the equator via the atmosphere.”
Contrasting experiments with and without a realistic ocean representation show the authors that improved inflow of cold underground water in the eastern tropical Pacific is able to communicate Arctic cooling to the tropics, thereby strengthening trade winds.
An important consequence of the results is that reducing uncertainty in simulated extratropical climate can also lead to improved simulation of climate in the tropics. The model hierarchy developed by the authors can be used to further explore two-way interactions between the tropics and the polar regions both for future climate forecasts as well as for interpreting climate state reconstructions in the geological past.
Fidelity of El Nino simulation means something to predict future climate
“Response circulatory response to extratropical radiation forcing” Scientific progress (2020). DOI: 10.1126 / sciadv.abd3021
Provided by the University of Hawaii at Manoa
Citation: A long-distance connection: Polar climate affects trade winds in the tropics (2020, November 20) Retrieved November 21, 2020 from https://phys.org/news/2020-11-distance-polar-climate-affects-strength.html
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