Influence of Anomalous Low-level Circulation on the Kuroshio in the Luzon Strait during ENSO


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The variation of Kuroshio loop in the Luzon Strait is important for the momentum, heat, and salt budgets of the SCS basin. Regarding the ENSO effects on the Kuroshio in the Luzon Strait, previous studies primarily focused on the effects of basin-scale wind anomalies and remote effects from the tropics. In this study, numerical experiments are conducted to demonstrate that the anomalous low-level circulation over the Philippine sea during El Niño weaken the northeasterly monsoon and favor the development of mesoscale eddies at the same time. This is caused by the increased baroclinic instability in the Subtropical Countercurrent (STCC)/North Equatorial Current region. Our results are supported by the long-term observational data. Consequently, the Kuroshio pattern in the Luzon Strait during El Niño tends to be more unsteady. During La Niña, the Kuroshio loop is enhanced in response to strengthened northeasterly winds. Overall, basin-scale wind curl anomalies in the North Pacific associated with El Niño increase westward Kuroshio transport in the Luzon Strait, whereas those associated with La Niña reduce it. The basin-scale wind anomalies induce the oceanic responses, resulting in the change of Luzon strait transport associated with Rossby waves generated during the adjustment process. The regional wind anomalies associated with El Niño enhances baroclinic instability. The former process (i.e., basin-scale wind anomalies) is barotropic and can be approximately as the steady state. However, the latter process (regional anticyclonic wind anomalies) is baroclinic, which includes strong nonlinearity that can only be resolved in the high-resolution model simulation.

Further information can be found in Prof. Tseng’s recent paper published in Ocean modelling (Kuo and Tseng., 2020).

Kuo, Y. C., & Tseng, Y. H. (2021). Influence of Anomalous Low-level Circulation on the Kuroshio in the Luzon Strait during ENSO. Ocean Modelling 159 (2021): 101759.