Dynamics and mixing of stratified rotating bottom boundary layers

在成层盆地中，倾斜底部地形附近的湍流增强对近底流的动力学有重要影响，并且通常对于盆地尺度混合也是必不可少的。普遍的观点是，近底湍流主要是通过破碎的内波或底部摩擦来激发的。 然而，最近DFG项目的结果表明，底部边界层中的差异平流可能产生重力不稳定层结，从而触发湍流对流。这一过程在以前的研究中基本上被忽略了，但它为近底湍流提供了一个重要的额外能量来源，并对底边界层内的混合产生了许多重大影响。从以前的研究中获得的见解，只集中在非旋转系统，将在本提案中推广，包括地球自转的影响。 与以往对近底流动力学的研究不同，本项目将强调由于剪切诱导对流引起的近底湍流的作用及其对总体混合的影响。 为此，我们在湍流建模方面的专业知识将在不同类型的理想化数值模型的帮助下用于旋转底部边界层的分析。这些理论和数值研究将得到补充的一个已经存在的数据集的分析，描述剪切引起的对流在北美大陆架上的底部边界层。

Enhanced turbulence in the vicinity of sloping bottom topography in stratified basins has an important effect on the dynamics of near-bottom currents, and is often also essential for basin-scale mixing. The prevailing view has been that near-bottom turbulence is energized primarily through either breaking internal waves or bottom friction. Results from a recent DFG project, however, have shown that differential advection in the bottom boundary layer may generate gravitationally unstable stratification, therefore triggering turbulent convection. This process, largely ignored in previous studies, was shown to provide an important additional energy source for near-bottom turbulence with a number of significant consequences for mixing inside bottom boundary layers. Insights gained from this previous study, focusing only on non-rotating systems, will be generalized in this proposal by including the effect of Earth's rotation. In contrast to previous investigations of the dynamics of near-bottom currents, the present project will emphasize the role of near-bottom turbulence due to shear-induced convection, and its implications for overall mixing. To this end, our expertise in turbulence modeling will be used for the analysis of rotating bottom boundary layers with the help of different types of idealized numerical models. These theoretical and numerical investigations will be complemented by the analysis of an already existing data set describing shear-induced convection in the bottom boundary layer on the North American shelf.