海表面溫度(Sea Surface Temperature, SST)的分布為海氣交互作用重要的變數之一。過去的文獻指出，熱帶太平洋溫躍層深度的特徵與變異在季節到年際的時間尺度內，會影響海表面溫度的變化。受到赤道東風的影響，熱帶太平洋溫躍層的平均狀態在垂直上呈現西深東淺的結構。然而在東太平洋聖嬰年時，伴隨著赤道東風減弱，溫躍層深度會在東太平洋下降而西太平洋上升，使得溫躍層的西傾狀態較為平緩。但在中太平洋聖嬰年時，溫躍層西傾狀態則無太大變化。為了解在西太平洋地區(5°N-10°N, 140°E-160°E)溫躍層的變化，本研究使用ECMWF-ORAS3海洋模式資料中20°C等溫線深度代表溫躍層深度。文中檢驗了在西北太平洋區域三個可能驅動溫躍層變化的機制：局地風場變化驅動的艾克曼幫浦、赤道洋流間海水質量輻合輻散形成的湧升作用、以及遠程風場激發造成的羅士培波傳播。研究結果顯示，局地影響因素在東太平洋聖嬰年發展早期會造成溫躍層變化，在中太平洋聖嬰年則不會。由羅士培波所造成的遠程風應力只顯示在東太平洋聖嬰年有出現，在中太平洋聖嬰年則沒有看同樣的訊號。而赤道洋流間海水質量輻合輻散形成的湧升作用在兩種聖嬰年發展上皆不是主要的溫躍層舉升的因素。同時，海溫在此區冬、夏皆有增溫的長期趨勢，然而溫躍層深度在夏季有變深而在冬季卻略變為更淺的趨勢。
In the western Pacific, the thermocline is relatively deep and the climatological upwelling is weak. Yet during El Niño, the thermocline shoals in the western Pacific along with the weakened trade winds. Meanwhile, the sea surface temperature (SST) displays a cold anomaly over the western Pacific. Here we deploy a datasimulated ocean model data, ECMWF ORA-S3 to study the thermocline variation in the western Pacific region (5°N-10°N, 140°E-160°E) where its interannual variability would impact the local SST variation. We examine three possible mechanisms driving thermocline displacement in the region: the local response to wind forcing via Ekman pumping, the current-related mass upwelling, and the propagation of upwelling Rossby waves generated by remote wind forcing. Our results show that, among the three mechanisms, it is mainly the Rossby waves excited in the centraleastern Pacific the dominant factor driving the thermocline displacement in Eastern-Pacific El Niño year except in the early developing stage the Ekman pumping contributes as well; however, there is no discernable wave propagating signal seen in Central-Pacific El Niño to make a certain statement. The dominant factor for thermocline displacement over the western Pacific region in Central-Pacific El Niño still requires further investigation. Our findings agree with other studies on that Central-Pacific El Niño might be less dependent on thermocline variations.
