多年期反聖嬰（Multi-year La Niña）事件對社會造成深遠影響，然而學界對其持續機制仍缺乏充分理解。本研究利用多變量經驗正交函數（MEOF）分析，針對 1998~2001 年（20 世紀）與 2020~2023 年（21 世紀）的兩次三重反聖嬰（Triple-dip La Niña）事件進行比較診斷，旨在釐清熱帶內部動力與外熱帶強迫（extratropical forcing）之相對貢獻。 研究結果揭示了海氣耦合主導層級發生了根本性的機制轉變。20 世紀的三重反聖嬰事件依循充放電（Charge-Discharge， CD）震盪機制的典型起始路徑，其中強烈的海洋熱含量釋放（discharge）與激發北太平洋經向模態（NPMM）的季節性足跡（SF）機制共同作用，觸發了該事件。然而，儘管起始訊號強烈，CD 機制最終未能有效終止冷相位。 相反地，21 世紀的事件顯著偏離此一路徑，其發生於微弱的熱含量釋放狀態下，且傳統 CD 機制表現出延遲的負回饋，主動抑制了相位的轉換。取而代之的是，該事件史無前例的持久性是透過增強的 Bjerknes 反饋與南太平洋經向模態（SPMM）的結合所達成。雖然 SF 機制在 21 世紀事件中缺乏持續的前兆驅動力，但 SPMM 躍升為主導驅動因子，其特徵為強烈的異常跨赤道南風。NPMM 與 SPMM 訊號之間被識別出的「反對應（anti-correspondence）」關係進一步支持了此一轉變，反映出一種非對稱且非同步的跨半球協同作用，有效地鎖定了冷海溫異常。這些發現表明，來自南半球的中緯度強迫可能已成為維持現代多年期反聖嬰事件的主要因素，補償了傳統充放電循環的失效。;Multi-year La Niña events exert profound societal impacts， yet their persistence mechanisms remain poorly understood. This study conducts a comparative diagnosis of the 1998–2001 (20th-century) and 2020–2023 (21st-century) triple-dip La Niña events using Multi-variate Empirical Orthogonal Function (MEOF) analysis to disentangle internal tropical dynamics versus extratropical forcing. Our results reveal a fundamental regime shift in the hierarchy of air-sea coupling. The 20th-century triple-dip La Niña event followed the canonical initiation of the Charge-Discharge (CD) oscillator， where strong oceanic discharge acted in concert with the Seasonal Footprinting (SF) Mechanism triggering the North Pacific Meridional Mode (NPMM). However， despite this robust onset， the CD mechanism failed to effectively terminate the cold phase. In contrast， the 21st-century event deviated significantly from this pathway， emerging from a weak discharge state where the classic CD mechanism exhibited delayed negative feedback that actively disfavored a phase transition. Instead， its unprecedented longevity was achieved through a strengthened Bjerknes feedback in conjunction with the South Pacific Meridional Mode (SPMM). While the SF mechanism lacked a sustained precursory drive in the 21st-century event， the SPMM emerged as the dominant driver， characterized by intense anomalous cross-equatorial southerly winds. This shift is further supported by an identified "anti-correspondence" between NPMM and SPMM signals， reflecting a non-symmetric and asynchronous inter-hemispheric synergy that effectively anchored the cold anomalies. These findings suggest that extratropical forcing from the Southern Hemisphere has potentially emerged as a primary sustainer of modern multi-year La Niña events， compensating for the breakdown of traditional discharge cycles.
