| 摘要: | 本研究透過簡單海洋同化模式(Simple Ocean Data Assimilation，簡稱為SODA)的再分析資料，深入分析不同種類聖嬰事件的動力機制。首先根據Niño3 (5°S-5°N, 150°-90°W)和Niño4 (5°S-5°N,160°E-150°W)指數，本研究將1950－2010聖嬰事件分為三類，其中包含海溫暖化接近東太平洋Niño3區域的東太平洋聖嬰事件、海溫暖化接近Niño4區域的中太平洋聖嬰事件，以及兼具以上兩種特徵的混合型聖嬰事件。根據發展期暖化的特徵，混合型聖嬰又可以進一步被分類為混合型-1和混合型-2聖嬰事件，其中混合型-1聖嬰事件有從東太平洋浮現並往中太平洋延伸的暖化發展，而混合型-2聖嬰事件則在中太平洋及東太平洋同時有相近的暖化特徵。
本研究進一步利用Bjerknes Feedback過程分析溫躍層、海表面溫度和表面風應力以測試其大氣與海洋的交互作用，其中溫躍層變化在混合型-1聖嬰事件發展期間從東太平洋區域浮現，然而西風應力距平僅在東太平洋事件持續向東發展；而混合型-2聖嬰事件中溫躍層變化在發展期僅分布於接近中太平洋區域，並在成熟期向東發展。進一步分析由聖嬰事件暖階段中，赤道區域的暖水堆積和向赤道兩側的南北向Discharge洋流；及冷階段中，赤道兩側的暖水堆積和向赤道的Recharge洋流相繼交替形成的Recharge Oscillator機制，並利用混合層熱含量收支方程分析海洋動力的暖化貢獻，其中混合型-1的洋流及暖水堆積於發展期在東太平洋浮現後開始向中太平洋發展，東太平洋區域則在向中太平洋發展後短暫的減弱，在成熟期後再度開始增強，赤道的暖水及Discharge洋流也在東太平洋溫躍層增厚後開始增強，並在成熟期達到最大值。熱含量收支方程中溫躍層回饋項及東西向洋流的暖化貢獻項皆可以看到由東太平洋浮現並向中太平洋發展的趨勢，並在成熟期於中太平洋有暖化的極值；混合型-2聖嬰事件暖水在發展期已在中太平洋浮現，該階段赤道區域則無明顯暖水堆積，而向東及Discharge洋流僅在成熟期於東太平洋增強。其熱含量收支方程中溫躍層回饋項及東西洋流暖化貢獻都於較早期有微弱的發展，僅在成熟期時向東太平洋擴張並增強。
根據目前整理出的四種聖嬰動力機制，本研究進一步分析近年2014－16聖嬰事件，該事件為一多年期且仍然可發展出強暖化的獨特聖嬰事件，相較於普遍認為其具有混合型聖嬰事件的發展，本研究分析其暖化型態發現該事件為由混合型-2聖嬰轉為東太平洋聖嬰的獨特事件。2014聖嬰事件發展期有相當強的動力及暖化快速發展，並在該階段過後快速減弱，至成熟期僅有微弱和逐漸向東擴張的暖化，進入2015後西風應力距平快速的增強，東太平洋的強暖化隨之開始浮現，轉為相當強的東太平洋聖嬰事件，而在成熟期過後暖化則快速的衰退。
;In this study, the ocean dynamics processes in developing the Mixed type of El Niño event with surface warming developed in both eastern and central Pacific have been analyzed systematically by reanalysis data from Simple Ocean Data Assimilation (SODA). Following the Niño index method (Kug et al., 2008), El Niño events from 1950 to 2010 are classified into three types of El Niño including Eastern Pacific El Niño (EP), Central Pacific El Niño (CP) and Mixed type El Niño (MIX) by directly comparing Niño3 (5°S-5°N, 150°-90°W) and Niño4 (5°S-5°N,160°E-150°W) indices. According to different warming patterns in the developing phase, it could be found that MIX El Niño can be further divided into MIX-1 El Niño with its surface warming emerging from the eastern Pacific and developing toward the central Pacific, and MIX-2 El Niño features a similar warming pattern between central and eastern Pacific.
Several mechanisms have been found in two types of Mixed El Niño, which could lead to different physical performances. In Bjerknes feedback mechanism, the air-sea interaction of MIX El Niño shows that westly wind stress is confined over the central Pacific, shifting the surface warming in both two types of MIX El Niño further west. However, the thermocline anomaly in MIX-1 emerged from eastern Pacific and developed toward central Pacific, while the one in MIX-2 remained weak near central Pacific, then strengthened in eastern Pacific in mature phase. In recharge-discharge mechanism and Heat budget analysis also reveals that MIX-1 El Niño started the discharge process early, and ocean dynamical processes such as eastward currents and surface heat content shifted westward. On the other hand, MIX-2 El Niño only shows weak eastward currents and surface heat content in its developing phase and strengthened in eastern Pacific during the mature phase. However, MIX-2 showed almost no discharge development in mature phase.
Furthermore, as a special strong multi-year El Niño case and a popular topic for ENSO research these days, the 2014-16 event was analyzed following the method in this study. It began as MIX-2 El Niño with a strong 2014 developing phase warming, and turned into EP El Niño with a strong warming pattern in eastern Pacific after the year 2015. |
