Parameterizing Nonpropagating Form Drag over Rough Bathymetry

Klymak Jody M.; Balwada Dhruv; Garabato Alberto Naveira; Abernathey Ryan

摘要

Slowly evolving stratified flow over rough topography is subject to substantial drag due to internal motions, but often numerical simulations are carried out at resolutions where this "wave'' drag must be parameterized. Here we highlight the importance of internal drag from topography with scales that cannot radiate internal waves, but may be highly nonlinear, and we propose a simple parameterization of this drag that has a minimum of fit parameters compared to existing schemes. The parameterization smoothly transitions from a quadratic drag law (similar to hu(0)(2)) for low Nh/u(0) (linear wave dynamics) to a linear drag law (similar to h(2)u(0)N) for high Nh/u(0) flows (nonlinear blocking and hydraulic dynamics), whereNis the stratification, h is the height of the topography, and u(0) is the near-bottom velocity; the parameterization does not have a dependence on Coriolis frequency. Simulations carried out in a channel with synthetic bathymetry and steady body forcing indicate that this parameterization accurately predicts drag across a broad range of forcing parameters when the effect of reduced nearbottom mixing is taken into account by reducing the effective height of the topography. The parameterization is also tested in simulations of wind-driven channel flows that generate mesoscale eddy fields, a setup where the downstream transport is sensitive to the bottom drag parameterization and its effect on the eddies. In these simulations, the parameterization replicates the effect of rough bathymetry on the eddies. If extrapolated globally, the subinertial topographic scales can account for 2.7TW of work done on the low-frequency circulation, an important sink that is redistributed to mixing in the open ocean.

机译：在粗糙地形上慢慢发展的分层流量由于内部运动而受到大量的阻力，但通常在该分辨率下进行数值模拟，其中必须参数化“波”拖动。在这里，我们突出了内部拖动从地形的重要性不能辐射内部波，但可能是高度非线性的，并且我们提出了一个简单的参数化，与现有方案相比，该拖动的简单参数化具有最小的拟合参数。参数化从二次拖拉法平稳地转换（类似于胡（0）（2 ））对于低NH / U（0）（线性波动态）到线性阻力法（类似于H（2）U（0）N）的高NH / U（0）流（非线性阻塞和液压动态），分层，H是地形的高度，U（0）是近底速度;参数化没有对科里奥利频率的依赖性。在具有合成碱基测量和稳态强制的通道中进行的模拟表明T.当通过减少地形的有效高度，考虑到降低的附近混合的效果，他的参数化准确地预测跨越广泛的强制参数。还测试参数化在生成Mescle eDDy字段的风力驱动信道流的模拟中，该设置在下游传输对底部拖动参数化和其对eDDIES的影响。在这些模拟中，参数化复制了粗糙度沐浴物对漩涡的影响。如果在全球外推，子内地形尺度可以占低频循环所做的2.7TW，这是一个重要的水槽，它被重新分配到在开阔的海洋中混合。

Parameterizing Nonpropagating Form Drag over Rough Bathymetry

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