On the Role of Bottom Pressure Torques in Wind-Driven Gyres
On the Role of Bottom Pressure Torques in Wind-Driven Gyres
复制标题
风驱动环流中底部压力扭矩的作用
DOI：
10.1175/jpo-d-20-0147.1
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发表时间：
2021
影响因子：
3.5
通讯作者：
Solodoch, Aviv
中科院分区：
文献类型：
--
作者：
Stewart, Andrew L.;McWilliams, James C.;Solodoch, Aviv
以往的研究表明，当在纬度带上积分时，海洋环流中的风输入涡度被底压力矩（BPT）平衡。然而，当在等深线包围的任何区域上积分时，BPT必须消失。这一约束引起了关于BPT应关闭涡度预算的区域的模糊性，并意味着为平衡局部风应力旋度而产生的BPT需要产生补偿的非局部BPT，从而产生非局部环流。本研究的目的是澄清的作用，BPT在风驱动的涡旋使用理想化的等密度模式。在一个封闭的，倾斜的盆地中进行的实验表明，BPT平衡的风应力旋度时，集成在纬度带。积分超过其他的，动力驱动的定义的环流，如正压流线，产生风应力旋度和底部摩擦力矩之间的平衡。这意味着底摩擦在构造环流中起着不可忽视的作用。非本地的底部压力扭矩表现在沿坡压力梯度的形式与弱流域尺度环流，并与过渡到风应力和底部摩擦之间的平衡在海岸周围。最后，一套扰动实验被用来研究BPT的动力学。为了预测BPT，作者扩展了以前的理论，该理论描述了表面压力信号从环流内部沿沿着行星位涡等值线向海岸的传播。这个理论被证明是同意密切诊断的贡献，涡度预算在整个套件的模型实验。
Previous studies have concluded that the wind-input vorticity in ocean gyres is balanced by bottom pressure torques (BPT), when integrated over latitude bands. However, the BPT must vanish when integrated over any area enclosed by an isobath. This constraint raises ambiguities regarding the regions over which BPT should close the vorticity budget, and implies that BPT generated to balance a local wind stress curl necessitates the generation of a compensating, nonlocal BPT and thus nonlocal circulation. This study aims to clarify the role of BPT in wind-driven gyres using an idealized isopycnal model. Experiments performed with a single-signed wind stress curl in an enclosed, sloped basin reveal that BPT balances the windsonlywhen integrated over latitude bands. Integrating over other, dynamically motivated definitions of the gyre, such as barotropic streamlines, yields a balance between wind stress curl and bottom frictional torques. This implies that bottom friction plays a nonnegligible role in structuring the gyre circulation. Nonlocal bottom pressure torques manifest in the form of along-slope pressure gradients associated with a weak basin-scale circulation, and are associated with a transition to a balance between wind stress and bottom friction around the coasts. Finally, a suite of perturbation experiments is used to investigate the dynamics of BPT. To predict the BPT, the authors extend a previous theory that describes propagation of surface pressure signals from the gyre interior toward the coast along planetary potential vorticity contours. This theory is shown to agree closely with the diagnosed contributions to the vorticity budget across the suite of model experiments.
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