Study Reveals How ENSO’s Impact on Asian-Western Pacific Climate Would Change under Global Warming

Chinese Academy of Sciences
The impact of El Niño on East Asian climate under a warmer climate will be dominated by the change in El Niño decaying pace, according to a study led by the Institute of Atmospheric Physics (IAP) of the Chinese Academy of Sciences.
The study was published in Journal of Climate on June 6.
The western North Pacific anomalous anticyclone (WNPAC) is a low-level atmospheric circulation system, linking up El Niño events with East Asian-western Pacific summer climate. The WNPAC can persist from El Niño mature phase in boreal winter to the upcoming summer, bringing abundant moisture to enhance the precipitation over East Asia.
How the WNPAC will change in the future concerns millions of people living in the East Asian-western Pacific region, but the future change in the WNPAC under global warming is highly uncertain across climate models.
The researchers found that about 23% of the uncertainty in WNPAC projection was attributed to the El Niño amplitude change while the rest 77% was from non-amplitude change, which is mainly related to the change in El Niño decaying pace, according to ZHOU Tianjun, the corresponding author of the study.
ZHOU, a senior scientist at IAP, is also a professor at the University of Chinese Academy of Sciences (UCAS).
To separately quantify the contributions of El Niño amplitude change and non-amplitude change from the total uncertainties, the researchers developed a new decomposition method. “This method is based on large ensemble climate simulation. We have used the output of 40-member large ensemble from the Community Earth System Model Large Ensemble project,” said WU Mingna, the first author of the study, who is a Ph. D student from the UCAS.

Schematic illustrates the relative contributions of change in different El Niño characteristics to the total uncertainties of the western North Pacific anomalous anticyclone projection. D(0)JF(1) and JJA(1) represent El Niño mature winter and decaying summer. (Image by WU Mingna and CHEN Xiaolong)

“A larger El Niño amplitude can enhance the WNPAC through a stronger tropical Indian Ocean capacitor effect under a warmer climate, while a faster El Niño decaying pace can also enhance the WNPAC through descending Rossby waves in response to colder than normal sea surface temperature over the tropical central-eastern Pacific, and vice versa,” said Dr. CHEN Xiaolong from IAP, co-author of the study.
“In addition to El Niño amplitude, more attention should be paid to the influence of other El Niño characteristics in climate system. Our decomposition method can be used to diagnose the origin of uncertainty related to El Niño in climate projections, as well as the relevant mechanisms,” said WU.
This work was jointly supported by the National Natural Science Foundation of China and National Key R&D Program of China.
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