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

通过对涡分辨模式（网格尺寸<10 km; R-grid）和涡允许模式（网格尺寸20 km; P-grid）的模拟结果进行比较，分析了R-grid模式比P-grid模式更能模拟海洋气候的原因。在湍流扩散格式的框架下，发展了亚网格输运的参数化方法。在P网格模式中进行了参数化处理，结果表明，在R网格模式（NPERM 5）中，副热带模态水和副热带逆流的模拟效果较好，而在P网格模式（NPERM 15）中，副热带模态水和副热带逆流的模拟效果较差，NPERM 5比NPERM 15能更好地模拟中间盐度极小值。由于冷的淡水和温暖的盐水混合强烈激活了R-网格模式中的一些类似于小波浪扰动的涡诱导厚度扩散系数和等密度扩散系数估计在Oyashio-黑潮混合水域。在P网格模型中，系数的幅值一般小于R网格模型。在R-网格模式中，等密系数大于厚度，因此P-网格模式不能模拟盐度极小值的主要原因是等密混合很弱。将R-网格上的变量分解为P-网格上的空间平均值及其距平，可以计算P-网格下的次网格输运。建立了与密度水平SGT相一致的三维反对称混合张量。亚网格的热量和盐度输运可以通过对应于该张量的扩散通量来实现。在P-网格模式中实现的参数化激活了等密混合并改善了结果。

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.