On roles of mesoscale variability and fresh water flux on deep water formation

随着时间尺度变长，海洋对气候变率的影响也越来越大。格陵兰海形成的北大西洋深水形成了全球深海传送带，其存在和形成速度影响着全球气候。根据来自北冰洋的淡水和海冰的数量，格陵兰海的表层不能变得足够稠密，无法与下层对流。然而，由冰形成的盐水排斥可能增加表层密度并产生深对流。表层在水平方向上不是均匀的，但在10-100km的空间尺度上具有变异性。水平变率是深层对流的另一个重要方面，因为对流可以发生在分层较弱的地区。除了开阔水域的深层对流外，在陆架区域形成了致密水，导致了中深度的北极水。本文建立了一个冰-海耦合模型。我们的目标是在模型中重建致密水的形成，以及理解对流、中尺度涡旋和内波等几个重要过程。该模型应用于拉布拉多陆架和鄂霍次克海，用于模拟海冰的季节性形成/衰减以及密集水的形成。使用非流体静力模型，我们检查了由开放引线和多裂谷中冰形成引起的垂直混合。稠密水取决于开阔水域的大小、分布和运动。认为斜压不稳定在向近海输送稠密水的过程中起主要作用。研究发现，在稳定平流层化的海洋中，内波对垂直混合很重要。这些结果为预测全球气候变化提供了有用的信息。

As a time scale becomes longer, the ocean plays more important roleson climate variability. The North Atlantic Deep Water formed in the Greenland Sea originates the global conveyor belt in the deep ocean, andits presence and formation rates influence global climate. The surface layr of the Greenland Sea could not become dense enough to be convected with the lower layr, depending on the amount of fresh water plus sea ice from the Arctic Ocean. However, brine rejection from ice formation may increase the surface layr density and yield deepconvection. The surface layr is not horizontally uniform, but contains variability at spatial scales of 10-100km. The horizontal variability is another important aspect for deep convection, because convection can occur in more weakly stratified areas. In addition to open water deepconvection, dense water is formed over the shelf regions, leading to the Arctic Water at the mid-depth.A coupled ice-ocean model was constructed in the present study. We aimed at reconstructing dense water formation in the model as well as understanding several important processes such as convection, mesoscale eddies and internal waves. The model was applied to the Labrador Shelf and the Okhotsk Sea, for simulating seasonal formation/decay of sea ice along with dense water formation. Using a nonhydrostatic model, we examined vertical mixing caused by ice formation in open leads and polynyas. The dense water is dependent on sizes, distribution and movement of the open water areas. It was suggested that baroclinic instability plays a major role in transporting dense water to the offshore region. Internal waves were found to be important for vertical mixing in a stably stratofied ocean. These results provide useful information for predicting global climate change.