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首页> 外文期刊>Journal of Physical Oceanography >Transient Tidal Circulation and Momentum Balances at a Shallow Inlet
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Transient Tidal Circulation and Momentum Balances at a Shallow Inlet

机译：浅水口的瞬态潮汐环流和动量平衡

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An analysis of transient momentum balances is carried out to elucidate circulation, dynamics, and exchange mechanisms at shallow barotropic tidal inlets. Circulation is computed using a depth-integrated, fully nonlinear, time-stepping, finite-element model with variably spaced grids having horizontal resolution down to 50 m. Velocity and elevation fields from the model are used to directly evaluate the contribution of each term in the momentum equations to the overall momentum balance. A transformation of the x―y momentum terms into an s―n coordinate system is used to simplify the interpretation of the dynamics and provide vivid illustrations of the forces and resulting accelerations in the flow. The analysis is conducted for an idealized inlet and contrasted with a highly detailed model of Beaufort Inlet, North Carolina. Results show that momentum balances in the immediate vicinity of these inlets vary significantly in time and space and oscillate between two dynamical states. Near maximum ebb or flood, the alongstream momentum balances are dominated by advective acceleration, pressure gradient, and bottom friction. Cross-stream balances are dominated fay centrifugal acceleration and pressure gradients. Near slack, balances more closely follow linear wave dynamics, with local accelerations balancing pressure gradients, and (to a lesser degree) Coriolis. Comparisons between the idealized inlet and Beaufort Inlet show broad similarities in these momentum balances. However, natural inlet geometry and bottom topography, as well as the tidal transmission characteristics of the sounds behind Beaufort Inlet produce strong asymmetries. Moreover, momentum balances are highly localized, often with subkilometer length scales. The dynamics are used to explain the physical mechanisms for inlet exchange. In particular, the results indicate that the cross-stream dynamics generate a "wall" along the length of an inlet during the stronger phases of the tide. The wall is established by opposing cross-inlet pressure gradients and centrifugal forces, and it poses a significant barrier to cross-inlet exchange during the stronger phases of the tide but is absent near slack.
机译：对瞬态动量平衡进行了分析，以阐明浅层正压潮汐进口处的环流，动力学和交换机制。使用深度积分，完全非线性，时间步长的有限元模型计算循环，该模型具有可变间隔的网格，水平分辨率低至50 m。该模型的速度场和高程场用于直接评估动量方程中每个项对整体动量平衡的贡献。将x-y动量项转换为s-n坐标系可简化动力学的解释，并生动地说明力和流中的加速度。该分析是针对理想的进样口进行的，并与北卡罗莱纳州的Beaufort进样口的详细模型进行了对比。结果表明，这些进气口附近的动量平衡在时间和空间上有很大变化，并且在两个动力学状态之间振荡。接近最大潮汐或洪水时，沿岸动量平衡主要由平流加速度，压力梯度和底部摩擦力决定。横流平衡主要是离心加速度和压力梯度。接近松弛时，平衡更紧密地遵循线性波动力学，局部加速度平衡压力梯度和（在较小程度上）科里奥利。理想进气口和Beaufort进气口之间的比较显示出这些动量平衡具有广泛的相似性。但是，自然的进气口几何形状和底部地形以及Beaufort进气口背后的声音的潮汐传播特性会产生强烈的不对称性。此外，动量平衡高度局部化，通常具有亚千米长度刻度。动力学用于解释入口交换的物理机制。特别地，结果表明，在潮汐的更强阶段，横流动力学沿着入口的长度产生了“壁”。该壁是通过相反的交叉入口压力梯度和离心力建立的，在潮汐较强的阶段，它对交叉入口的交换构成了很大的障碍，但在松弛时几乎没有。

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