| 摘要: | 聖嬰現象 (El Niño Southern Oscillation，簡稱ENSO) 是一個位於赤道太平洋區域並具有週期性之氣候現象，其不僅對南北半球熱帶區域的天氣發揮一定的調節作用，同時也會對其他地區以及各個氣候因子產生遙相關的影響，因此研究各種可能導致ENSO發生的因子是極具重要性的課題，其有助於藉由提高ENSO的預測能力來精進氣象預報之準確度並以此來影響人類生活。過往研究顯示於春季的北極震盪 (Arctic Oscillation，簡稱AO) 可能會透過綜觀尺度的渦流活動來影響西風產生進而促進ENSO形成，而本篇研究後續將會針對不同相位的春季AO對聖嬰事件造成的差異進行討論，並探索相關的機制。
此篇研究發現春季AO在不同相位下可能會透過不同方式激發西風異常，正相位如前人研究會傾向激發低緯度氣旋式異常，並因此引發太平洋經向模態 (Pacific Meridional Mode，簡稱PMM) 相關之機制出現與緯向平流作用增強，對後續成熟期的海面溫度在接近中太平洋之區域影響顯著，然而，負相位會傾向透過向赤道的波列傳播來間接引發西風異常，並主要通過緯向平流作用來使接近中太平洋之區域的海面溫度相對於沒有春季AO的條件下有增暖的情形，此外，不同的春季AO相位對同年度的聖嬰事件於強度以及持續時間上，連同隔一年的聖嬰相位皆會有所差異，由負春季AO相位所引發的聖嬰事件在強度與時間下皆會較正相位時弱，但其有助於隔年的反聖嬰事件接續出現，相對而言，正春季AO雖會傾向形成較強且較久的聖嬰事件，但對接續之聖嬰相位的轉換則相較負相位具有較高的變異性。最後，本篇研究也執行了動力與熱力的收支分析，揭示在春季AO的作用下基本上會由緯向平流作用主導聖嬰的發展，而熱力則會透過短波輻射與潛熱通量的調節主導衰退的進行。
;El Niño Southern Oscillation (ENSO) is a quasi-periodic climate phenomenon over the equatorial Pacific area. It not only influences the weather in both Northern and Southern tropics, but also affects diverse climatic factors through teleconnections. As a result, examining the factors responsible for the initiation of El Niño is a critical issue. It is conducive to improving ENSO predictability and advancing the accuracy of weather forecasts. Previous studies have illustrated that the spring Arctic Oscillation (AO) initiates the ENSO pattern via synoptic scale eddy feedback that can modulate the equatorial westerly wind anomalies. Therefore, this study will further analyze the varying El Niño responses to the spring AO phases and explore the mechanisms involved.
This study reveals that the ways in which the El Niño-like pattern and the westerly wind anomalies are generated under the respective spring AO conditions are contrasting. During the positive spring AO phase, the low-latitude cyclonic circulation anomalies, along with the tropical westerly and southwesterly wind anomalies, tend to form. These anomalies, in turn, trigger the Pacific Meridional Mode (PMM)-related mechanism and enhance the zonal advective feedback. They also reinforce the significant impacts on the sea surface temperature anomalies (SSTA) near the central Pacific at the subsequent mature stage. By contrast, the negative spring AO pattern tends to produce an equatorward wave train-like pattern to modulate the tropical westerly wind anomalies (Deng and Dai, 2024). Of note, compared to the neutral spring AO, the negative spring AO warms the SSTA near the central Pacific predominantly through zonal advective feedback. In addition, the positive spring AO tends to produce stronger and longer El Niño events. However, the induced subsequent ENSO phase associated with the positive spring AO exhibits relatively large variability. During the negative spring AO phase, the occurrence of weaker and shorter El Niño events is more likely. In the subsequent winter, a La Niña event tends to develop. This research also conducts the dynamic and thermodynamic analysis. It suggests that under the effect of spring AO, the development stage of El Niño is dominated by the zonal advective process, whereas the decaying stage is mainly governed by the modulation of shortwave radiation and latent heat fluxes. |
