Impacts of Equatorial Ocean Currents on El Ni�o Simulations in CMIP6 Models

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Title:	Impacts of Equatorial Ocean Currents on El Ni�o Simulations in CMIP6 Models
Authors:	林育慎;Lin, Yu-Shen
Contributors:	大氣科學學系
Keywords:	聖嬰—南方震盪現象;第六階段耦合模式對比計畫;赤道洋流;混合層熱收支分析;El Niño–Southern Oscillation;Coupled Model Intercomparison Project Phase 6;Equatorial ocean currents;Mixed layer heat budget analysis
Date:	2022-08-03
Issue Date:	2022-10-04 10:47:47 (UTC+8)
Publisher:	國立中央大學
Abstract:	近幾十年來，氣候模式對於聖嬰—南方震盪現象（El Niño–Southern Oscillation，簡稱ENSO）的模擬能力已有明顯的進步，不過在許多海氣耦合環流模式（Coupled general circulation model，簡稱CGCM）裡仍存在一種常見的模擬誤差：於聖嬰—南方震盪現象 (ENSO) 的成熟期時，海表面溫度距平會有過於向西擴展的結構。於是本研究便使用了14個參與第六階段耦合模式對比計畫（Coupled Model Intercomparison Project Phase 6，簡稱CMIP6）的海氣耦合環流模式（CGCM），利用其中的歷史情境（historical run），探討在成熟期的聖嬰（El Niño）事件中，赤道洋流對於海表面溫度距平的主要影響。藉由模擬結果，我們發現在長時間氣候平均態下，向西的緯向洋流在赤道中太平洋地區的模擬過強，導致當聖嬰發展時，向東的緯向洋流距平會在赤道東太平洋地區明顯減弱，其距平最大值發生的區域便會更靠近太平洋西側的海洋大陸。接著透過混合層的熱收支分析（mixed layer heat budget analysis），可以觀察到模式會在赤道西太平洋地區模擬出過大的zonal advective feedback，進而引發較大的正混合層溫度距平，最後造成在暖池區域有較暖的海表面溫度距平，而這樣的誤差會使第六階段耦合模式對比計畫（CMIP6）中的模式傾向呈現出與中太平洋聖嬰架構較為類似的聖嬰事件。因此，若要模式模擬出較為接近真實結構的聖嬰，在赤道太平洋中有良好的緯向洋流表現會是不可忽略的關鍵因素。;Great advances have been made in the skill of climate models for simulating El Niño–Southern Oscillation (ENSO) diversity in the recent decades. Nonetheless, there is a common modeled bias existing in many coupled general circulation models (CGCMs) that a westward extension of sea surface temperature anomaly (SSTA) pattern takes place during the ENSO mature phase. This study used the historical run of 14 CGCMs participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6) to explore the substantial influences of equatorial ocean currents on the SSTA in the peak phase of El Niño. With respect to an excessive climatological westward ocean currents over the equatorial central Pacific in the models, the eastward ocean current anomalies were found to become much weakened across the equatorial eastern Pacific with their maximum shifting toward the maritime continent during the El Niño developing phase. Therefore, models tend to simulate a stronger zonal advective feedback in the equatorial western Pacific, which can be evaluated through a mixed layer heat budget analysis. This biased zonal advective feedback ultimately induces an unrealistic positive mixed layer temperature anomaly tendency and leads to a relatively warm SSTA in the warm pool region. Such an SSTA bias could favor a more central–Pacific El Niño–like structure in CMIP6 models. The realistic simulations of ENSO evolution may sensitively rely upon reasonable simulations of the zonal ocean currents over the equatorial Pacific region.
Appears in Collections:	[Department of Atmospheric Sciences and Graduate Institute of Atmospheric Physics ] Department of Earth Sciences

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