Quantification of shear-induced convection and bottom-boundary mixing in natural waters

许多作者指出，通过湖泊和海洋微结构剖面技术获得的垂直混合估计值一般不能解释全球物质和热量收支所表明的总混合。寻找其他混合机制，边界混合已被确定为一个关键过程。在这项研究中，由重力不稳定的底部边界层（BBL）驱动的边界混合过程进行了研究。这种不稳定的BBL在稳定分层的盆地是强大的上坡电流的结果，通常是由湖泊内部的假潮或长的内部惯性波在沿海海洋。由于在湍流底界中，上坡速度随着与沉积物的距离增加而增加，底界中的重水（即冷水或盐水）可能会平流到较轻（即较暖或较新鲜）的水上方，导致对流混合。不稳定的下坡电流导致混合的抑制。我们计划用跨学科的方法来研究这个过程：我们的主要研究地点将是博登湖，在那里将详细研究BBL动力学和湍流的湖沼学设置。我们的海洋学研究地点将是波罗的海，在那里发生了类似的混合过程。数值湍流模型将用于分析测量点的这一过程，研究流域效应，并构建通用理论。

It has been pointed out by numerous authors that estimates of the vertical mixing obtained by microstructure profiling techniques in lakes and the ocean can, in general, not explain the total mixing suggested by the global budgets of matter and heat. Searching for additional mixing mechanisms, boundary mixing has been identified as a key process. In this study, a boundary mixing process driven by a gravitationally unstable bottom boundary layer (BBL) is investigated. Such unstable BBLs in stably stratified basins are the result of strong up-slope currents, typically caused by internal seiching in lakes or by long internal-inertial waves in the coastal ocean. Due to the fact that in a turbulent BBL, the up-slope speed increases with increasing distance from the sediment, heavy (i.e. cold or salty) water in the BBL may be advected above lighter (i.e. warmer or fresher) water, leading to convective mixing. Inversely, down-slope currents lead to a suppression of mixing. We plan to investigate this process with an interdisciplinary approach: our primary study site will be Lake Constance, where the BBL dynamics and turbulence will be studied in detail for a limnological set-up. Our oceanographic study site will be the Baltic Sea, where a similar mixing process takes place. A numerical turbulence model will be used to analyze this process at the measuring sites, study the basin-wide effect, and construct a general theory.