Comparison of entrainment in overflows simulated by z-coordinate, isopycnal and non-hydrostatic models☆
Comparison of entrainment in overflows simulated by z-coordinate, isopycnal and non-hydrostatic models☆
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DOI：
10.1016/j.ocemod.2004.11.006
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发表时间：
2006
期刊：
影响因子：
3.2
通讯作者：
S. Legg;R. Hallberg;J. Girton
中科院分区：
文献类型：
--
作者：
S. Legg;R. Hallberg;J. Girton
一系列理想化的数值模拟稠密的水流过一个广泛的均匀的斜坡，采用z坐标模式（麻省理工学院的大气环流模式）和等密度坐标模式（Hallberg等密度模型）。计算进行了几个不同的水平和垂直分辨率，并为一系列的物理参数。一个子集的计算进行了非常高的分辨率，使用非流体静力学的MITgcm的变体。在所有的计算中，稠密的水在夹带并与环境流体混合的同时沿着斜坡下降。卷吸，混合和下坡下降的分辨率和垂直坐标的依赖性进行了评估。在非常粗糙的分辨率下，z坐标模型会产生过多的虚假混合，稠密的水很难沿着斜坡下降。然而，在中间分辨率的z坐标模型中的混合是低于发现在高分辨率的非流体静力学模拟，和稠密的水下降进一步下降的斜坡。等密度线计算显示较少的分辨率依赖性，虽然夹带和混合都略有减少，在粗糙的分辨率。在中间分辨率的z坐标和等密度模型产生类似的混合和夹带水平。这些结果提供了一个基准，对未来的发展溢流夹带参数化的z坐标和等密度模型可以进行比较。
A series of idealised numerical simulations of dense water flowing down a broad uniform slope are presented, employing both a z-coordinate model (the MIT general circulation model) and an isopycnal coordinate model (the Hallberg Isopycnal Model). Calculations are carried out at several different horizontal and vertical resolutions, and for a range of physical parameters. A subset of calculations are carried out at very high resolution using the non-hydrostatic variant of the MITgcm. In all calculations dense water descends the slope while entraining and mixing with ambient fluid. The dependence of entrainment, mixing and down-slope descent on resolution and vertical coordinate are assessed. At very coarse resolutions the z-coordinate model generates excessive spurious mixing, and dense water has difficulty descending the slope. However, at intermediate resolutions the mixing in the z-coordinate model is less than found in the high-resolution non-hydrostatic simulations, and dense water descends further down the slope. Isopycnal calculations show less resolution dependence, although entrainment and mixing are both reduced slightly at coarser resolution. At intermediate resolutions the z-coordinate and isopycnal models produce similar levels of mixing and entrainment. These results provide a benchmark against which future developments in overflow entrainment parameterizations in both z-coordinate and isopycnal models may be compared.