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Yu-Lin Eda Chang National Taiwan Normal University Critical wind condition and current reversals in the Taiwan Strait Co-author: L.-Y. Oey, Y.-C. Lin, M.-C. Chang, and S. Varlamov

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2012/03/15 2012/04/01 Shipwreck incident near Xiamen Debris were found at Tauyuan 50 200 Mean Transport : 1.8 Sv Winter:0.9 Sv [Wang et al, 2003] Winter: 0.12Sv [Lin et al, 2005] Why and how could the cross-strait flow occur during northeasterly monsoon ?

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Tracer simulation with/without Stoke drift No wave With wave Difference

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Analytical model: Follow the quasi-steady, depth average: rv A = -g / y + oy /H r ~ 1.610 -5 (s -1 ) / y ~ -4.510 -7 u o = -(g/f). / y + oy /(f E ) v o = -(g/r). / y + oy /(f E ).[1 + f E /(Hr)] Critical Along-Strait Wind v o =0, v oy ~ -1.210 -4 (m 2 s -2 ) [~ -10m/s] u o =0, u oy ~ -0.6810 -4 (m 2 s -2 ) [~ -7m/s]

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EOF analysis : mode 1 Corr( oy (v o ), PC)=0.83Corr( oy (v o ), PC)=0.93 v o = -(g/r). / y + oy /(f E ).[1 + f E /(Hr)]

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u ~ u PG + u wind + u PG v o = -(g/r). / y + oy /(f E ).[1 + f E /(Hr)] v m ~ v o + v oPG Corr(PC uv, Vo PG )=0.61 Corr(PC , Vo PG )=0.70 Corr( oy, PC)= 0.68Corr( oy, PC)= 0.52 EOF analysis : mode 2

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Summary Flow tends to be southwestward if the Northeasterly wind stress is stronger than |1.210 -4 | m 2 s -2 Flow tends to be northeastward if the Northeasterly wind stress is weaker than |0.6810 -4 | m 2 s -2 The model tracer-tracking simulations support such a scenario, and it demonstrates the importance of wave-induced Stokes drift in advecting the debris to the near-coast regions The first two modes of EOF account for 70~85% total variance. The first mode explains the quasi-steady pressure gradient and wind forced velocity. The second mode is affected by the fluctuating pressure gradient

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ATOP - Advanced Taiwan Ocean Prediction System Resolution: 0.1 x0.1 deg x 41 sigma levels Free Running from 1987 to 2011 Forecast: 2012/Jan-present NCEP-GFS wind, -7days hincast~7days forecast (No data assimilation on the shelf) Oey, et al, 2012

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