Black Lake Big Bend High Resolution Numerical Simulation

As a west boundary current of North Pacific Subtropical Gyre, theKuroshio transport a huge mount of heat from the lower latitude to themiddle and high latitude. It behaves like a multiple equilibrium statein the region south of Japan. At certain time, the Kuroshio will stayin either a far from shore large meander path or a near shore nonlargemeander path. The water taken by the Kuroshio are much warmer than thosebeyond its ways, so its path states and transitions are very importantto local climates.The study used Regional Ocean Modeling System (ROMS), with2004～2006high frequency CORE2forcing&flux fields and the simultaneous HYCOMassimilation dataset as the boundaries to simulate the whole westernPacific in a0.1fine resolution. Regions south of Japan are studiedin details. Through the compares between forcings (boundaries) withand without interannual signal in them, the effect by atmosphere andthe westward propagation of Rossby wave at30N) to the regional SSHvariability are confirmed. The PN, TK, Asuka,137Eand PT sectionin-situ data from Japan Meteorological Agency are used to verify themodel result. The model seems to handle the Asuka line transport (whichcan determine the multiple state) well.Going through10experiments, the sensitivity of south Japan Kuroshiomultiple equilibrium state to the horizontal mixing scheme are re-searched. The viscous coefficient in the movement equations and thediffusive coefficient in the tracer equations have similar ability toattenuate the sea surface variability in the ocean region south ofJapan. When the coefficients are too low, the Kuroshio will stay a lotof time in large meander path. When they are too high, the Kuroshiowill never show a large meander path. With appropriate values, thestatistical time frequencies of large meander and nonlarge meander willagree well with the observation. The paper shows the transition progress from the large meander tononlarge meander with or without eddy interacting, and the transitionprogress from the nonlarge meander to the large meander with or withouteddy shedding. Mechanism of the large meander transition is discussed.Result shows a nonlocal control of the Kuroshio transport and a localdissipation of negative relative vorticity south of Japan pay a privaterole to the long-term large meander state. Meanwhile the various shapesand lifespans of westward propagating eddies under different horizontalmixes hold response for the different short-term large meander events.Based on the parameterization studied above, in helps of coupledatmospheric and oceanic anormaly information outputted from CCSM3, thepaper also gives a reasonable method to forecast the future Kuroshiomeander states in years2080～2099, and have some early results.