利用海洋環流模式探討黑潮親潮延伸流域之能量轉換過程

Abstract

由於在黑潮和親潮延伸流域(Kuroshio-Oyashio Extension)其複雜的鋒面結構內蘊含許多可用的潛在位能，這些潛在位能可以藉由不穩定的機制來進行能量轉換。而這些能量會改變黑潮區域的動量和熱量的傳送而進一步影響大氣。觀測的資料中顯示此區域的海表面高度和海平面溫度的距平值震盪的週期從季內震盪到年代際震盪。為了更近一步了解不穩定性和黑潮的關係，本研究中利用日前研發採用高效能平行化方法之台灣多重尺度全球海洋環流模式，討論在準平衡狀態下的全球及區域結果。此外，本模式可以完整模擬中尺度海洋的現象，對黑潮親潮的交互作用也有和觀測一致的表現，因此本篇研究中除了利用傳統定義距平場的方式來討論模式中的渦流結構，也利用培養法(Breeding method)來探討黑潮親潮流域不穩定度的發展性。利用在模式中加入適當之培養向量(Bred vector)，並藉由反覆重置培養向量疊加在控制背景場中，透過非線性模式及不同尺度不穩定發展的特性，自然地將模式內之快速發展模保留下來，並濾除不相關的雜訊。從實驗結果的主成分分析可以知道不穩定發生的密集區域在日本外海，也知道黑潮區域的不穩定性主要來自渦流和平均流交互作用所產生的能量轉換，以及藉由垂直密度的差異將可用位能釋放所產生的能量轉換有關。

The Kuroshio-Oyashio Extension (KOE) involves significant barotropic and baroclinic energy conversion due to complex frontal instability. The energy conversion changes the sea surface momentum and heat flux, and further affects the local air-sea interaction. The observed sea surface height and sea surface temperature anomalies exhibit considerable variances from interannual to decadal time scales in the KOE region. To investigate the link between energy conversion and Kuroshio Extension, we simulated the KOE variability using an eddy-permitting global ocean circulation model, based on the recently-developed TaIwan Multi-scale Community Ocean Model (TIMCOM) with parallel implement. The model fully resolved the mesoscale features in the global framework, including the quasi-steady solution and the Kuroshio-Oyashio interaction . We further applied the breeding method to investigate the KOE flow instability. The approach added the rescaled bred vector into the control experiment to explore the development of fast growing mode in the KOE region. We applied the Empirical orthogonal function to find the principle component of KOE instability around east coastal of Japan, and the energy conversion in KOE region is result from the interaction of mean flow and the eddy as well as the available potential energy released form vertical density perturbation.