Spatial And Temporal Characteristics Of The North Pacific Low-latitude Western Boundary Current And Variation Of Research

As connecting the tropical and subtropical ocean circulations, North Pacific Low Latitude West Boundary Currents (NPLLWBC) play a very important role in the meridional transport of mass, heat and salt in the world ocean. Studies on the spatial and temporal characteristics of NPLLWBC as well as its mechanism are significant in practice.Spatial and temporal characteristics of NPLLWBC as well as its variation are analyzed by using fifty-year numerical outputs from high eddy-resolving simulations of OFES (OGCM for the Earth Simulator). The results are as follows.The characteristics of the spatial structure of the NMK systems can be well described by the OFES data compared to Simple Ocean Data Assimilation (SODA). The variability of the eddy structure in the source area of the Kuroshio, MUC, LUC and the eastward current under the NEC is well described, too. The spatial structure of the system and the flux are consistent with the observed data.The NEC, KC and MC transport have a strong seasonal, interannual and interdecadel signal. Spectrum analysis indicates that NMK transport chiefly has a seasonal oscillation with a three-month to six-month period, an interannual oscillation with 2a and 2-7a ENSO period and an interdecadal variation with a period more than 10 years. On the interannual scale, the frequency spectrum of the variation is rather broad. The NEC and KC transport is dominated by ENSO period with 2-7 years, and the MC transport is dominated by a quasi-biennial oscillation.The NEC and MC have a seasonal maximum transport in spring (May) and a minimum transport in fall (November). The KC has a maximum transport in spring (April), minimum in winter (January), and the fall takes the secondary. The NEC and the KC vary in the same phase, while the KC and MC vary in the contrary phase except in winter.On interannual timescale, the NEC is positive correlated to KC (MC). The NEC transport variation determines the KC and MC transport. The NMK transport is closely related with ENSO. The correlation between the distribution rates of the KC and MC transport is negative, which is affected by ENSO and NEC bifurcation latitude. When the El Nino happens, the NMK transport decreases, the bifurcation latitude moves northward, the distribution rates of the KC transport is less and the distribution rates of the MC transport is more. The situation is reversed while the La Nina happens. It has a larger influence on the NEC and KC transport than on the MC transport.The NMK transport decreases evidently after a step change at the end of the 70th decade of last century. NEC, KC and MC transports decrease obviously. The decrease is mainly account for the strengthened El Nino after the 80th decade. The decrease of the NEC transport determines the variation of the KC and MC transport. Besides, the NEC bifurcation latitude has a long trend of moving northward after climate change, with the distribution rate of KC and MC transport increases and decreases, respectively.