The Dynamic of EP and CP El Ni�o under the Influence of Atlantic Multi-decadal Oscillation

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题名:	The Dynamic of EP and CP El Ni�o under the Influence of Atlantic Multi-decadal Oscillation
作者:	劉祉筠;Liu, Tzu-Yun
贡献者:	大氣科學學系
关键词:	大西洋多年代際震盪;大西洋多年代際震盪;Atlantic multi-decadal oscillation;El Niño-southern oscillation
日期:	2023-07-18
上传时间:	2024-09-19 14:11:22 (UTC+8)
出版者:	國立中央大學
摘要:	大西洋多年代際震盪(Atlantic multi-decadal oscillation, 簡稱AMO)的效應將透過遙相關的方式影響太平洋的平均狀態，進而改變聖嬰現象(El Niño)的表現。在AMO正相位時，東太平洋聖嬰將伴隨著較弱且緯度上分布較廣的暖水異常，並傾向於發展成多年的聖嬰事件；另一方面，當東太平洋聖嬰在AMO負相位時，則是有較強的暖水以及西風異常，但隨著聖嬰事件的衰弱，東太平洋漸漸轉為冷水異常，而發展為單一的聖嬰事件。至於在中太平洋聖嬰事件中，除了同樣在AMO負相位下有較強的海溫異常外，其發展也有較明確的差異。當中太平洋聖嬰處於AMO正相位時，暖水異常主要在赤道地區發展並持續至第二年；相較之下，AMO負相位下的中太平洋聖嬰，暖水自副熱帶地區傳遞至赤道地區，並在第二年開始衰退。由迴歸分析的結果中得到，AMO對於太平洋平均態的影響除了赤道信風的強弱外，在東北太平洋副熱帶地區對於海平面氣壓也有相對明顯的改變，AMO正（負）相位下，副熱帶地區的高（低）氣壓異常值，將影響東太平洋聖嬰在西太平洋引起的高壓強度及分布。在AMO正相位下，西太平洋高壓異常增強伴隨反氣旋式的環流，在中太平洋地區帶來東北風異常的分量並限制了聖嬰現象下西風異常的發展。而在AMO負相位下，由於西太平洋高壓異常減弱，其環流影響範圍較侷限於西太平洋地區，赤道太平洋的西風異常得以發展，並能產生較強的西風異常及聖嬰事件。此氣壓異常值也將影響中太平洋聖嬰下，於副熱帶產生的低壓異常，並改變西南風異常於該區於緯度上的分布。在AMO正相位下，較弱且分布偏北的低壓異常使得其氣旋式環流帶來的西南風處於較高緯度地區，故由西南風異常在副熱帶地區產生的風–蒸發–海溫 (wind–evaporation–SST，簡稱WES)效應不顯著，暖水異常主要在赤道附近發展。另一方面，在AMO負相位下，副熱帶低壓異常的增強使得其環流分布緯度較低，副熱帶地區產生西南風異常，伴隨WES 效應使得暖水異常隨著中太平洋聖嬰的暖水發展逐漸由副熱帶地區傳至赤道地區。 ;Atlantic multi-decadal oscillation (AMO) serves as a modification of the mean state of the Pacific through teleconnection which further impacts El Niño evolution. Under the positive AMO (+AMO) phase, the sea surface temperature anomaly (SSTA) shows a weaker intensity but a wider distribution for eastern Pacific (EP) El Niño in the meridional scale, and it tends to develop into a multi-year El Niño. On the contrary, EP El Niño shows stronger SSTA as well as westerly anomaly and it comes with a La Niña-like SSTA distribution as El Niño wanes under the negative AMO (–AMO) phase. As for the result of central Pacific (CP) El Niño, aside from the duration and intensity difference of SSTA under two phases of AMO, the evolution of SSTA also shows a distinguishable pattern. The warm SSTA develops within the tropics in the +AMO phase while the SSTA evolves from the subtropics in the –AMO phase. Our result demonstrates that aside from the strength of westerly anomaly, the greatest difference lies in the sea level pressure anomaly around the north-eastern subtropics which would alter the amplitude and distribution of the eastward-extending anomalous high pressure in the western Pacific in EP El Niño. During the +AMO phase, the high pressure anomaly in the western Pacific is enhanced with the stronger anti-cyclonic circulation. The associated north-easterly anomaly around the central Pacific then reduces the westerly anomaly related to EP El Niño. In contrast, the weakened high pressure anomaly in the western Pacific brings a weakened north-easterly anomaly to the equatorial region under the –AMO phase that contributes to an intensified westerly anomaly and a stronger EP El Niño intensity. As for the result of CP El Niño, the intensity of the subtropical low pressure anomaly mainly adjusts the south-westerly anomaly in the subtropics. Under the +AMO phase, the weaker subtropical low pressure anomaly is located slightly northward and the associated south-westerly anomaly is less influential to the subtropical area. Consequently, weaker wind-evaporation-SST (WES) feedback is observed and the evolution of warm SSTA is limited within the tropics. In contrast, the subtropical low pressure anomaly is strengthened under the –AMO phase. The stronger south-westerly anomaly then causes the stronger WES feedback and has the heat transported from the subtropics to the tropics.
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