On the influence of the parameterization of lateral boundary layers on the thermohaline circulation in coarse-resolution ocean models
On the influence of the parameterization of lateral boundary layers on the thermohaline circulation in coarse-resolution ocean models
复制标题
粗分辨率海洋模型中横向边界层参数化对温盐环流的影响
DOI：
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发表时间：
1999
期刊：
影响因子：
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通讯作者：
A. Verdière
中科院分区：
文献类型：
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作者：
T. Huck;A. Weaver;A. Verdière
由于海洋内部存在一阶地转平衡，在粗分辨率海洋环流模型中，侧向边界层参数化比粘度参数化对温盐翻转和深水特性的影响更大。在笛卡尔坐标、平底、β 平面的行星地转海洋环流模型中实施了动量耗散和相关边界条件的不同公式，并恢复了表面密度和零风应力的边界条件。具有无滑移边界条件的传统拉普拉斯摩擦会产生与地转和斯维尔德鲁普平衡非常一致的内部环流，但会在横向边界处产生非常大的垂直（穿流）输送，特别是西部边界流中的上升流和东北角的下降流。经向和纬向翻转因此而增强，但将不像深对流区域那样冷的表层水驱入深处。在非法向流边界条件框架内，瑞利摩擦力与各种摩擦闭合对沿岸速度的影响，通过允许撞击海岸的地转流的水平再循环，有效地减少了沿边界的二重垂直输送。因此，这些参数化会导致较弱的翻转，较冷的深水和较尖锐的温跃层导致较高的向极地热传输。我们认为，沿边界的上升流是粗分辨率动力学的结果，而不仅仅是水平扩散的结果（称为维罗尼斯效应，一旦等重线被沿海上升流倾斜，水平扩散就会产生大量的二重通量）。横向边界层的替代参数化可以减少这种影响，而无需沿等密度线旋转混合张量。该模型比较证明需要清楚地评估西部边界流中的底重上升流的程度，并开发基于物理的横向边界层参数化，以提高粗分辨率 OGCM。
Because of the first order geostrophic balance in the ocean interior, the parameterization of lateral boundary layers has more influence than the parameterization of viscosity on the thermohaline overturning and the deep water properties in coarse-resolution ocean circulation models. Different formulations of momentum dissipation and associated boundary conditions are implemented within a planetary-geostrophic ocean circulation model for a Cartesian coordinate, flat-bottomed, β-plane, with restoring boundary conditions for the surface density and zero wind stress. Traditional Laplacian friction with a no-slip boundary condition produces an interior circulation in good agreement with geostrophy and the Sverdrup balance, but generates very large vertical (diapycnal) transports at lateral boundaries, especially upwelling in the western boundary current and downwelling in the northeast corner. The meridional and zonal overturning are thus enhanced, but drive to depth surface waters that are not as cold as the ones in the deep convection regions. Rayleigh friction with various frictional closures for the alongshore velocities within a no-normal-flow boundary condition framework efficiently reduces the diapycnal vertical transports along the boundaries, by allowing horizontal recirculation of geostrophic currents impinging into coasts. Hence, these parameterizations induce weaker overturnings, with colder deep water and a sharper thermocline resulting in higher poleward heat transports. We suggest that the upwelling along the boundaries is a consequence of the coarse-resolution dynamics and not only horizontal diffusion (termed the Veronis effect, horizontal diffusion produces large diapycnal fluxes once the isopycnals are tilted by coastal upwellings). Alternative parameterizations for the lateral boundary layers reduce this effect without the need for rotating the mixing tensor along isopycnals. This model comparison proves the need to clearly assess the extent of the diapycnal upwelling in the western boundary currents and to develop physically-based parameterizations of lateral boundary layers in order to improve coarse-resolution OGCMs.