| 摘要: | 本研究旨在探討大西洋多年代際振盪（Atlantic Multi-decadal Oscillation, 簡稱AMO）對 La Niña 演化的調控機制，特別聚焦其透過副熱帶太平洋與印度洋所引發的不同海氣交互作用，進一步理解AMO如何影響熱帶太平洋溫躍層結構、海溫分布與大氣環流異常，發現AMO在不同位相會顯著改變La Niña的發展時程、持續性與衰退機制。La Niña可依據冷海溫異常的位置大致分為中太平洋型（central Pacific, CP-type）與東太平洋型（eastern Pacific, EP-type），前者冷水集中於換日線附近，後者則偏向南美洲沿岸。AMO正相位下，La Niña通常發展較晚，冷海溫異常發展後延伸至次年，出現雙峰式冷事件結構，其空間型態趨近於中太平洋型（CP-type）La Niña。相反地，在AMO負相位下，La Niña於次年快速衰退，且其冷海溫異常的空間型態趨近於東太平洋型（EP-type）La Niña，並符合充放電振盪理論（recharge oscillator theory）中所描述的振盪行為。進一步檢視赤道太平洋低層風場與溫躍層異常變化可發現，在AMO正相位時期，赤道太平洋存在顯著的東風異常與西深東淺的溫躍層傾斜結構，然而此結構未如理論所預期轉為充電階段（recharge phase），而是在次年持續維持放電（discharge）狀態，使得冷海溫異常延續，La Niña被迫持續發展。相比之下，AMO負相位時期的風場與溫躍層變化較為對稱，符合充電階段的補償機制，海溫異常得以自然緩解。
此外，印度洋的變異性在AMO不同相位下亦有顯著差異，進一步影響 La Niña的強度與持續時間。AMO正相位時期，由於西太平洋強東風異常增強沃克環流，加強了印度洋東風異常與西深東淺的溫躍層結構，藉此強化印度洋自身的獨立變異性，削弱了ENSO–IOD關係，無法有效透過大尺度的海氣耦合促進La Niña的衰退，使La Niña更為持久。而在AMO 負相位期間，西太平洋的東風異常較弱，對沃克環流的增強作用有限，使得印度洋的東風異常與溫躍層傾斜結構不如正相位明顯。這樣的結構加強ENSO–IOD關係，使La Niña快速衰退。
;This study investigates the regulatory mechanisms through which the Atlantic Multidecadal Oscillation (AMO) influences the evolution of La Niña events, with a particular focus on the distinct air-sea interactions triggered by the subtropical Pacific and the Indian Ocean. Via analyzing how the AMO modulates thermocline structures, sea surface temperature anomalies (SSTA), and atmospheric circulation anomalies in the tropical Pacific, our findings show that different AMO phases significantly alter the timing, persistence, and decay mechanisms of La Niña. La Niña events can generally be categorized into central Pacific (CP-type) and eastern Pacific (EP-type) types, based on the location of maximum cold SSTAs—near the dateline for CP-type and closer to the South American coast for EP-type. Under the positive AMO (+AMO) phase, La Niña events tend to develop later and exhibit a double-peaked cold SSTA that persists into the following year. The spatial structure of the SSTA tends to resemble the Central Pacific (CP)-type La Niña. However, La Niña events under the negative AMO (-AMO) phase decay more rapidly, and the spatial pattern of the SSTA resembles the eastern Pacific (EP)-type La Niña, consistent with the oscillatory behavior described by the recharge oscillator theory. Further examination of equatorial Pacific thermocline and lower-level wind anomalies reveals that, under the +AMO phase, pronounced easterly anomalies and a strongly tilted thermocline structure dominate. However, this configuration fails to transition into a recharge phase as expected, instead remaining in a discharge state during the subsequent year, thereby prolonging the La Niña event. In contrast, under the -AMO phase, wind and thermocline anomalies are more symmetric, supporting the recharge process and facilitating the natural decay of SSTA.
Moreover, the variability of the Indian Ocean also differs significantly between AMO phases, further influencing the intensity and duration of La Niña. Under the +AMO phase, enhanced easterly anomalies in the western Pacific intensify the Walker circulation, strengthening the easterly wind anomalies and thermocline slope in the Indian Ocean. This reinforces the Indian Ocean′s internal variability and weakens the ENSO–IOD relationship, thereby limiting the effectiveness of large-scale air-sea coupling in promoting La Niña decay and resulting in prolonged cold events. Conversely, the -AMO phase is associated with milder easterly wind anomalies over the western Pacific, which suppress the enhancement of the Walker circulation and lead to a reduced thermocline inclination in the Indian Ocean. The resulting configuration enhance the ENSO–IOD connection, promoting a more rapid termination of La Niña. |
