A new approach to parameterizing ocean eddies: energetics, conservation and flow stability

海洋中存在着一个强有力的涡流场。这些涡旋是大气中天气系统的海洋模拟物，但由于海水和空气的密度不同，以及海洋和大气的垂直结构不同，它们发生在小得多的空间尺度上。海洋涡旋也在较长的时间尺度上演变，通常是几个月，并且可以在长达数千年的时间尺度上影响全球环流。因此，模拟海洋的全球环流是一项比大气更具挑战性的任务，因为必须捕获更大范围的空间和时间尺度。结果之一是，海洋气候模式通常“paramaterise”海洋涡旋，也就是说，而不是直接模拟涡旋，涡旋对大尺度环流的间接影响是通过修改海洋模式求解的方程来表示的。这是一项具有挑战性的任务，涡旋参数化是海洋气候预测中很大的不确定性的来源。该项目的目的是增进关于海洋涡旋如何影响大尺度海洋环流的知识，并改进涡旋参数化。特别是，我们的目标是开发方案，避免做我们知道是不正确的事情，例如引入虚假的能源。通过确保我们的涡流参数化符合基本的物理原理，例如能量守恒和角动量（其中一个例子大致相当于南极洲周围循环的水量），我们相信我们可以对海洋涡流可以做什么和不能做什么提供重要的限制。新的涡流参数化将在最先进的计算海洋模型上进行测试。

The ocean is populated by a vigorous eddy field. These eddies are the oceanic analogue of weather systems in the atmosphere, but occur on a much smaller spatial scale due to the different densities of seawater and air, and differences in the vertical structure of the ocean and atmosphere. Ocean eddies also evolve on longer time scales, typically months, and can effect the global circulation on time scales up to millennia. Hence modelling the global circulation of the ocean is a much more challenging task than the atmosphere due to the greater range of spatial and temporal scales that must be captured. One consequence is that ocean climate models usually 'paramaterise' ocean eddies, that is, rather than simulate the eddies directly, the indirect effect of the eddies on the larger-scale circulation is represented by modifying the equations that are solved by the ocean model. This is a challenging task and eddy parameterisations are a source of great uncertainty in ocean climate projections. The aim of this project is to developed improved knowledge of how ocean eddies influence the large-scale ocean circulation and to developed improved eddy parameterisations. In particular, we aim to develop schemes that avoid doing things that we know are simply incorrect, such as introducing spurious sources of energy. By ensuring that our eddy parameterisations are consistent with fundamental physical principles, such as conservation of energy and angular momentum (an example of which loosely equates to the amount of water circulating around Antarctica), we believe that we can provide significant constraints on what ocean eddies can and cannot do. The new eddy parameterisations will be tested on a state-of-the-art computational ocean model.