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首页> 外文期刊>Journal of Physical Oceanography >Structure of the Circulation Induced by a Shoaling Topographic Wave
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Structure of the Circulation Induced by a Shoaling Topographic Wave

机译：浅化地形波引起的环流结构

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The structure of the potential vorticity flux and a mean flow induced by a topographic wave incident over a bottom slope are investigated analytically and numerically, with focus on the case that bottom friction is the dominant dissipation process. In this case it is shown that the topographic wave cannot be a steady source of the potential vorticity outside the bottom Ekman layer. Instead, the distribution of potential vorticity is determined from the initial transient of the topographic wave. This potential vorticity and the heat flux by the topographic wave at the bottom determine the mean flow and give a relation between the horizontal and vertical scales of the mean flow. When the horizontal scale of the mean flow is larger than the internal deformation radius and the potential vorticity is not so large, the mean flow is almost constant with depth independent of whether the topographic wave is bottom intensified. Then the mean flow is proportional to the divergence of the vertically integrated Reynolds stress. This divergence, which is caused by bottom friction, is large when the group velocity c_g and the vertical scale μ~(-1) of the wave motion are small. Thus, the mean flow tends to be large where c_g and μ~(-1) become small and decreases as the topographic wave is dissipated by bottom friction. Because bottom friction also dissipates the mean flow, the mean flow asymptotically approaches a constant value as the friction becomes zero. These features of the potential vorticity flux and the mean flow are reproduced in numerical experiments in which it is also shown that the distribution of the mean flow depends on the amplitude of the wave because of the Doppler shift of the wave by the mean flow. These features of the mean flow are preserved when stratification and bottom topography resembling those over the continental slope near the Gulf Stream are used. The transport of the mean flow is about 20 Sv (Sv ≡ 10~6 m~3 s~(-1)) when the wave amplitude is about 2 cm s~(-1). This transport is similar to that of the recirculation gyre in the Gulf Stream region.
机译：通过对底部摩擦是主要耗散过程的情况进行了分析和数值研究，研究了势旋量通量的结构以及由入射到底部斜坡上的地形波引起的平均流量。在这种情况下，表明了地形波不能成为底部埃克曼层外部潜在涡旋的稳定来源。取而代之的是，根据地形波的初始瞬变确定潜在涡度的分布。这种潜在的涡度和底部地形波的热通量决定了平均流量，并给出了平均流量的水平和垂直比例之间的关系。当平均流的水平尺度大于内部变形半径并且势涡不是那么大时，平均流几乎随深度恒定，而与地形波是否在底部增强无关。然后，平均流量与垂直积分雷诺应力的发散成比例。当波的群速度c_g和垂直方向μ〜（-1）较小时，由底部摩擦引起的发散较大。因此，平均流量在c_g和μ〜（-1）变小时趋于变大，并且随着地形波由于底部摩擦而消散而减小。由于底部摩擦也会耗散平均流量，因此当摩擦变为零时，平均流量渐近地接近恒定值。在数值实验中再现了潜在涡旋通量和平均流量的这些特征，其中还表明，由于平均流量引起的波的多普勒频移，平均流量的分布取决于波的振幅。当使用类似于墨西哥湾流附近大陆坡的分层和底部地形时，均流的这些特征得以保留。当波幅约为2 cm s〜（-1）时，平均流量的传输约为20 Sv（Sv≡10〜6 m〜3 s〜（-1））。这种运输方式与墨西哥湾流地区的再循环涡流相似。

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