Numerical study about heat and salinity transports induced by small disturbances in an ocean general circulation

比较了涡旋分辨模式(网格大小10 km；R网格)和涡旋允许模式(20 km；P网格)的模拟结果，以了解R网格模式比P网格模式更能模拟海洋气候的原因。在湍流扩散格式的框架下，发展了一个亚网格输送的参数化方法。副热带模式水和副热带逆流在R网格北太平洋模式(NPERM5)中模拟得比较逼真，而在P网格模式(NPERM15)中却不能很好地模拟。由于R网格模式中大量细丝状小尺度扰动对冷淡水和暖咸水黑潮混合的强烈激活，NPERM5模式比NPERM15模式能更好地模拟中等盐度极小值。在P网格模型中，系数的大小一般比R网格小。因此，在P网格模式中，盐度极小值不能被模拟的主要原因是该模式中的等温混合很弱。将R网格上的变量分解为空间平均值和P网格上的异常，可以计算P网格上的次网格输送(SGT)。建立了与密度的水平SGT一致的三维反对称混合张量。该张量对应的扩散通量可以实现次网格的热量和盐度输送。在P网格模式中实现的参数化激活了等周期混合，并改善了结果。

Results from an eddy-resolving model (grid-size<10km; R-grid) and an eddy-permitting model (20km; P-grid) were compared to understand the reason why R-grid model can simulate the ocean climatology better than P-grid. A parameterization of sub-grid transport was developed using the framework of turbulent diffusion scheme. The parameterization was implemented to a P-grid model and validated.The subtropical mode water and the subtropical countercurrent are realistically simulated in a R-grid North Pacific model (NPERM5), while they are poorly simulated in a P-grid model (NPERM15).The intermediate salinity minimum can be better represented in NPERM5 than in NPERM15, because cold fresh Oyashio water and warm saline Kuroshio water mix vigorously activated by numbers of filament-like small-wale disturbances in the R-grid model The eddy-induced thickness diffusivity and the isopycnal diffusivity coefficients were estimated in the Oyashio-Kuroshio mixed water region. The magnitudes of the coefficients are generally smaller in P-grid model than R-grid. The isopycnal coefficient is larger than thickness in the R-grid model Therefore, the primary reason why the salinity minimum cannot be simulated in P-grid model is the very weak isopycnal mixing in it.Decomposing the variables at R-grids into the spatial average and the anomalies from it over a P-grid, the sub-grid transport (SGT) fir the P-grid can be calculated. The three-dimensional anti-symmetric mixing tensor consistent with the horizontal SGT of density was formulated. The sub-grid heat and salinity transport can be realized through the diffusive flux corresponding to this tensor. The parameterization implemented in a P-grid model activates the isopycnal mixing and improves the result.