OceanBound

海洋中的洋流是湍流的，并且在比海洋盆地小得多的尺度上受“涡流变异性”的支配。这种复杂的、非线性的变化使得我们不可能全面了解整个海洋的所有细节——我们可以运行非常昂贵的高分辨率计算机模型，并得到看起来很真实的答案，但我们如何知道它们的长期预测是否也是现实的？这依赖于对所涉及的过程有一个很好的理解——我们必须找到一种方法来避开漩涡的复杂性，并找到系统的可理解方面，通过理论将模型与真实的海洋环流联系起来。幸运的是，当我们观察海洋的“侧壁”边界时，我们发现涡流效应被大大简化了，我们得到了整个海洋的图景，这可以与理论思想联系起来。这一项目的目的是通过少数几个明确界定的过程来了解全球海洋环流，从而增进对其对从海平面到热输送等一系列重要问题的影响的了解。在混乱的漩涡中，有一部分海洋环流在全球范围内运作，在不同的海洋盆地之间运送水，并在世界各地运送热量。这些模态是全球气候系统中最重要的部分。一种模式是大西洋经向翻转环流，它通过整个大西洋向北输送热量，对欧洲气候有很大影响。其他洋流还包括将温暖的海水从太平洋输送到印度洋的印尼通流，以及连接大西洋、印度洋和太平洋的南极环极洋流。与这些模态相关的洋流对世界各地的沿海海平面有影响，导致一些海岸的海平面比其他海岸高。我们把这些模式的影响称为海洋的“全球管道”。尽管我们的计算机模型可以很好地模拟海洋环流的许多方面，但很难模拟出这种管道如何随时间变化。对未来气候和海平面做出准确的预测需要我们了解变化的原因，而为了检验我们的理解，我们需要对过去的管道变化进行准确的测量。海洋的湍流使得测量如此大规模的模式变得非常困难。要测量洋流本身，就需要在海洋中随时放置大量的仪器。但我们现在知道，海洋侧壁上的压力编码了大尺度模式的信息，而没有湍流和涡流带来的混乱。仅在少数几个地方发生的过程就控制了很远的距离上的压力，因此也控制了管道。在这个项目中，我们将使用海洋模型来了解这些局部过程如何影响海洋边界压力，从而影响全球海洋管道。然后，新的认识将用于确定我们对未来哪些变化有信心，并指导下一代气候模型的改进。

The currents in the ocean are turbulent, and dominated by "eddy variability" on scales much smaller than the ocean basins. This complex, nonlinear variability makes it impossible to understand the ocean as a whole in all its detail - we can run very expensive computer models at high resolution and get realistic-looking answers, but how do we know whether their long-term predictions are also realistic? That relies on having a good understanding of the processes involved - we have to find a way to sidestep the complications of the eddies and find comprehensible aspects of the system to connect the models, via theory, to the real ocean circulation. Fortunately, when we look at the "sidewall" boundaries of the ocean, we find that the eddy effects are greatly simplified, and we get a picture of the whole ocean which can be connected to theoretical ideas.The aim of this project is to make the global ocean circulation comprehensible in terms of a small number of clearly defined processes, and hence to improve understanding of its influence on a range of important issues from sea level to heat transport.Amidst the eddying chaos, there are parts of the ocean circulation which operate on a global scale, carrying water between different ocean basins and carrying heat around the world. These modes are among the most important parts of the global climate system. One mode is the Atlantic Meridional Overturning Circulation, which transports heat to the north throughout the entire Atlantic Ocean and has a large effect on European climate. Others include the Indonesian Throughflow, which carries warm water from the Pacific to the Indian Ocean, and the Antarctic Circumpolar Current, which connects the Atlantic, Indian and Pacific oceans. The currents associated with these modes have an influence on coastal sea levels around the world, causing sea level to be higher along some coasts than others. We call the effect of these modes the "global plumbing" of the ocean.Although we have computer models which can simulate many aspects of the ocean circulation well, it is hard to model how this plumbing varies over time. Making good predictions of future climate and sea level requires us to understand the causes of variability, and to test our understanding we need good measures of how the plumbing changed in the past.The ocean's turbulence makes it very hard to measure such large scale modes. To measure the currents themselves would require an enormous number of instruments to be in the ocean at all times. But we now know that pressure on the sidewalls of the ocean encodes information about the large scale modes without the added confusion from turbulence and eddies. Processes occurring at just a few places control the pressures, and therefore the plumbing, over very large distances.In this project, we will use ocean modelling to learn how those local processes influence ocean boundary pressures, and hence the global ocean plumbing. The new understanding will then be used to determine which future changes we can have confidence in, and to direct improvements of the next generation of climate models.