Quantitative Assessment of Factors Controlling Mesoscale Eddy Penetration Across the Kuroshio in the Luzon Strait from Numerical Simulations

Hang Zhao¹ Xiaolin Bai¹ and Shengmu Yang^2
1State Key Laboratory of Marine Environmental Science, and College of Ocean and Earth Sciences, Xiamen University, Xiamen, China
²College of Meteorology and Oceanography, National University of Defense Technology, Changsha, China
Abstract
The Luzon Strait (LS) serves as the core pathway for multi-scale dynamic interactions and mass-energy exchange between the Kuroshio Current and the South China Sea (SCS). Mesoscale eddies contribute substantially to oceanic energy transfer and material transport. While most westward-propagating eddies in the Northwest Pacific are blocked by the strong horizontal shear of the Kuroshio east of the LS, a small fraction can penetrate across the Kuroshio and enter the SCS. To date, the individual and combined controls of eddy and Kuroshio properties on eddy penetration remain to be systematically quantified.
In this study, we use the MITgcm to numerically investigate the interaction between mesoscale eddies and the Kuroshio in the LS. A suite of sensitivity experiments is designed to quantify the regulatory effects of eddy intensity, eddy radius, as well as Kuroshio intensity and path pattern on eddy crossing across the Kuroshio. Results show that eddy penetration capacity is jointly determined by the nonlinear coherence of eddies and the dynamical state of the Kuroshio. Eddies with higher intensity and larger radius exhibit stronger structural robustness against shear-induced destruction, and thus have a higher probability of breaking through the Kuroshio barrier. Weaker Kuroshio intensity reduces its shearing and blocking effects, leading to elevated penetration success rates. In addition, the Kuroshio path plays a critical role: within the tested parameter range, no successful eddy penetration occurs when the Kuroshio takes the leaping path with no SCS intrusion.
This study provides a quantitative evaluation of multi-factors controls on eddy penetration across the Kuroshio in the LS, and offers numerical support for understanding the mesoscale dynamic linkage between the Northwest Pacific and the SCS, as well as cross-strait mass and energy exchange mechanisms.