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

许多作者已经指出，通过微观结构剖面技术在湖泊和海洋中获得的垂直混合估计，一般来说不能解释全球物质和热量预算所暗示的总混合。寻找其他混合机制，边界混合已被确定为一个关键过程。本文研究了重力不稳定底边界层驱动下的边界层混合过程。在稳定分层的盆地中，这种不稳定的BBLs是强大的上坡流的结果，通常是由湖泊的内部沉降或沿海海洋的长内部惯性波引起的。由于在湍流BBL中，上坡速度随着离沉积物距离的增加而增加，因此BBL中的重水（即冷水或咸水）可能会平流到较轻的水（即暖水或淡水）上方，从而导致对流混合。相反，下坡流导致混合抑制。我们计划用跨学科的方法来研究这一过程：我们的主要研究地点将是康斯坦斯湖，在那里，我们将详细研究湖沼学设置的BBL动力学和湍流。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点的这一过程，研究整个流域的影响，并建立一般理论。

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.