Three-dimensional perspective on a convective instability and transition to turbulence in an internal solitary wave of depression shoaling over gentle slopes
Three-dimensional perspective on a convective instability and transition to turbulence in an internal solitary wave of depression shoaling over gentle slopes
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缓坡浅滩内孤立波对流不稳定和湍流转变的三维视角
DOI：
10.1007/s10652-022-09844-7
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发表时间：
2022
影响因子：
2.2
通讯作者：
Thomsen, Greg N.
中科院分区：
文献类型：
--
作者：
Rivera-Rosario, Gustavo;Diamessis, Peter J.;Lien, Ren-Chieh;Lamb, Kevin G.;Thomsen, Greg N.
通过高精度、完全非线性和非静力模拟，在三维(3D)中探索了低压内孤立波的浅化。使用了时间平均的背景分层和野外观测的海流剖面，以及来自南中国海的实测水深数据。该计算方法基于一种高分辨率、高精度的变形谱多区域罚函数法和不可压流计算方法。最近在南海的现场观测表明，存在对流不稳定，随后是一个可能持续数十公里的次表层再循环核心，并驱动由湍流引起的混合，估计比通常在海洋中发现的大四个数量级。前一次对流不稳定是由于波传播速度突然减慢，低于水平波的最大诱发速度，可能是由于斜压背景流的近地表涡度层的伸展造成的。在这些观测的推动下，本研究审查了三维对流不稳定的开始，这种不稳定导致了次表层再循环核心的形成，因为ISW在垂直到等深方向传播和浅滩。在波动诱导的速度场和密度场中插入噪声场，以强制三维演化。初始失稳具有沿横向发展的过渡结构。将破碎波中横向不稳定的演化和随后向湍流的转变与现场观测到的结构波进行了比较。这样，我们就初步了解了内燃机内部再循环核心的形成，这是随后内部湍流、混合和粒子传输的驱动力。
The shoaling of an internal solitary wave (ISW) of depression is explored in three-dimensions (3D) through high-accuracy, fully nonlinear, and nonhydrostatic simulations. Time-averaged background stratification and current profiles from field observations, along with measured bathymetry data from the South China Sea (SCS), are used. The computational approach is based on a high-resolution and high-accuracy deformed spectral multidomain penalty method incompressible flow solver. Recent field observations in the SCS indicate the presence of a convective instability followed by a subsurface recirculating core that may persist for more than tens of km and drive turbulent-induced mixing, estimated to be up to four orders of magnitude larger than that typically found in the ocean. The preceding convective instability occurs due to a sudden decrease in the wave propagation speed, below the maximum horizontal wave-induced velocity, and possible from the stretching of the near-surface vorticity layer of the baroclinic background current from the propagating ISW. Motivated by such observations, the present study examines the onset of the 3D convective instability that results in subsurface recirculating core formation, as the ISW propagates and shoals in the normal-to-isobath direction. A noise field is inserted in the wave-induced velocity and density field to force the evolution in 3D. The initial instability has a transitional structure that develops in the lateral direction. The evolution of the lateral instability and subsequent transition to turbulence in the breaking wave is compared with the wave structured observed in the field. As such, a preliminary understanding of the formation of recirculating cores in ISWs, the driver for subsequent turbulence, mixing, and particle transport in the interior is obtained.
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