Abstract A parameterisation scheme for restratification of the mixed layer by submesoscale mixed layer eddies is implemented in the NEMO ocean model. Its impact on the mixed layer depth (MLD) is examined in 30-year integrations of “uncoupled” ocean-ice (GO5) and “coupled” atmosphere-ocean-ice-land (GC2) 1/4° global climate configurations used by the Met Office Hadley Centre. The impact of the scheme on the MLD in GO5 is up to twice as large in subtropical and mid-latitudes when the mixed layer Rossby radius is not limited to guard against CFL-type instabilities and excessively strong volume overturning. Such a limit is not found to be necessary for stable integration of the scheme in NEMO. An alternative form of the scheme is described that approximates the mixed layer Rossby radius as a function only of latitude. This formulation is more generally robust to instability and has a comparatively larger impact on the MLD than the original formulation, but yields qualitatively similar results. The global mean impact of the scheme on the MLD is found to be almost twice as large in 1° and 2° configurations of GO5 as it is in the 1/4° configuration. This is shown to be the result of the scheme overcompensating for the decay in strength of resolved mixed layer density fronts in this model with decreasing horizontal grid resolution. The MLD criterion defining the depth scale of the scheme is shown to affect its global mean impact on the MLD by nearly a factor of 3 in GO5 and GC2, depending on whether the criterion is chosen to capture the actively mixing layer or the well-mixed layer. The parameterisation reduces the magnitude of deep MLD biases while increasing the magnitude of shallow biases. The globally averaged winter MLD bias is reduced from 17% to 9% of climatological values in GO5 but changes from + 3 % to − 4 % in GC2. Summer mixed layers are too shallow on average in both configurations and their average magnitude is increased by the parameterisation.

中文翻译：

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NEMO 海洋模型中亚中尺度混合层涡流参数化对混合层深度的影响

摘要 在 NEMO 海洋模型中，实现了亚中尺度混合层涡旋对混合层重新分层的参数化方案。它对混合层深度 (MLD) 的影响在“非耦合”海冰 (GO5) 和“耦合”大气-海洋-冰地 (GC2) 1/4° 全球气候配置的 30 年整合中得到了检验。气象局哈德利中心。当混合层Rossby半径不限于防止CFL型不稳定性和过强的体积翻转时，该方案对GO5中MLD的影响在亚热带和中纬度地区的影响高达两倍。发现这样的限制对于在 NEMO 中稳定集成方案是不必要的。该方案的另一种形式被描述为将混合层罗斯比半径近似为纬度的函数。该公式通常对不稳定性更稳健，并且与原始公式相比对 MLD 的影响相对更大，但会产生质量相似的结果。发现该方案对 MLD 的全局平均影响在 GO5 的 1° 和 2° 配置中几乎是 1/4° 配置中的两倍。这被证明是该方案在水平网格分辨率降低的情况下对该模型中已分辨混合层密度锋的强度衰减进行过度补偿的结果。在 GO5 和 GC2 中，定义方案深度尺度的 MLD 标准显示其对 MLD 的全局平均影响接近 3 倍，这取决于选择标准是捕捉活跃混合层还是充分混合层。参数化降低了深 MLD 偏差的幅度，同时增加了浅偏差的幅度。全球平均冬季 MLD 偏差在 GO5 中从气候值的 17% 减少到 9%，但在 GC2 中从 + 3 % 变为 − 4 %。夏季混合层在两种配置中平均都太浅，参数化增加了它们的平均幅度。