Processes of breaking of large-amplitude unsteady lee waves leading to turbulence
Processes of breaking of large-amplitude unsteady lee waves leading to turbulence
复制标题
大振幅非定常背风波的破碎过程导致湍流
DOI：
10.1029/2012jc008160
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发表时间：
2013
影响因子：
--
通讯作者：
Nakamura Tomohiro
中科院分区：
文献类型：
--
作者：
Shoko Abe;Nakamura Tomohiro
利用具有真实地形的非静力垂直二维模型，研究了阿拉斯加Amchitka山口激发大振幅（~200 m）非定常背风波后向湍流的转变。该模型解决了比大振幅非定常背风波小两个阶的运动，该背风波在山脊的背风波中激发，并表明在山脊顶部附近和非定常背风波的第一个波谷下游的过渡过程是不同的。在脊顶附近，确定了三个过渡阶段。在第一阶段，对流开始于非定常背风波峰的上游侧（前向波破碎）和下游侧（后向波破碎）。在下一个阶段，Kelvin-Helmholtz（KH）波在静态不稳定区域和底部下坡流之间的增强剪切区域中发展。在最后阶段，Tollmien-Schlichting（TS）波在底部发展，位于KH波下方，并形成漩涡，最终破裂。据作者所知，这是第一篇报道海洋中后向波破碎的发生和TS波激发的可能性的文章。在非定常背风波的第一个波谷的下游，由于非定常背风波的逆压梯度，水流与底部分离。分离流形成准周期性脱落的涡流。KH和TS波的发展和气流分离以及由非定常背风波引起的翻转等密度线引起的对流增强了透壁混合。
The transition to turbulence after excitation of large‐amplitude (~200 m) unsteady lee waves in Amchitka Pass, Alaska, is investigated using a nonhydrostatic vertically two‐dimensional model with realistic topography. The model resolves motions two orders smaller than a large‐amplitude unsteady lee wave, which is excited in the lee of the ridge, and shows that transition processes near the ridge top and downstream of the first trough of the unsteady lee wave are different. Near the ridge top, three stages of transition are identified. In the first stage, convection begins on the upstream sides (forward wave breaking) and downstream sides (backward wave breaking) of the crests of the unsteady lee wave. In the next stage, Kelvin‐Helmholtz (KH) waves develop in regions of enhanced shear between statically unstable regions and downslope flow on the bottom. In the last stage, Tollmien‐Schlichting (TS) waves develop on the bottom, under the KH waves, and form vortices, which finally break down. To the best of the authors’ knowledge, this is the first paper to report on the occurrence of backward wave breaking and the possibility of TS wave excitation in the ocean. Downstream of the first trough of the unsteady lee wave, flow is separated from the bottom by an adverse pressure gradient attributed to the unsteady lee wave. The separated flow forms vortices, which are shed quasi‐periodically. Diapycnal mixing is enhanced by the development of KH and TS waves and flow separation, as well as by convection due to overturning isopycnals induced by the unsteady lee wave.