A summary on studies of western boundary current
system
in the North Pacific Ocean
(1.Institute of Marine Environment, Ocean University of China, Qingdao 266003, China;
2.Second Institute of Oceanography, SOA, Laboratory of Ocean Dynamic Processes and Satellite Oceanography, SOA, Hangzhou 310012, China)
Abstract: The North Equatorial Current (NEC)in the Pacific Ocean bifurcates as it approaches the Phillippine coast, feeding the northward flowing Kuroshio and the southward flowing Mindanao Current(MC). The NEC—Kuroshio—MC current system is important because of its role in the heat budget of the western Pacific 0cean warmpoo1 and its direct involvement in the global ocean thermocline circulation via the Indonesian throughflow ，both of which are believed to be essentia1 in determining the world’s climate. Also, the current system is a part of the shallow, meridional, wind and buoyancy—flux—driven circu1ation that directly connects the subtropica1 and equatoria1 oceans. Studies of the current system have significantly advanced our knowledge of its mass and heat transport, in particular with regard to its variations．In this paper，we give a summary of the main studies on western boundary current system in the North Pacific Ocean in 1atest twenty years in order to get more completely understanding of its structure and variations. The N’EC bifurcation is mainly controlled remotely by Rossby waves from the east，remotely by equatorward propagating coastal Kelvin like waves from the north，and locally by the East Asian monsoon，in which the Asian monsoon is the most important factor deciding the seasonal variation of the NEC bifurcation. Special attentions should be paid on the foil0wing key problems’that is，the NEC bifurcation latitude，mean transport and its variabilitv of the NM K current system, the seasonal and interannual variability of NEC bifurcation latitude，the relationship between the variability of NEC and ENSO, the role of the NMK current system in exchanging the tropical and subtropical water and the dynamic mechanism of the NEC bifurcation and the mean structure of the NMK current system. Though there are some difficulties such as short of data and no completely three dimensional numerical model with enough high resolution of the western boundary current system in the North Pacific Ocean in present research, it is still possible for us to understand the SCS circulation more clearly by further ocean investigation，four dimensional assimilation on a1l historical data, diagnostic analysis of physical mechanism with simple conceptua1 n1odel and numerical experiment considering all sorts of physical processes.
Key Words: the North Pacific Ocean; western boundary current; NEC bifurcation; Kuroshio; transport