High-resolution modelling of near-inertial waves in the ocean

海洋的密度分层和地球自转的结合导致了波的存在，称为惯性重力波，它通过海洋的整个深度传播，并对其能量做出了很大的贡献。惯性重力波的大部分能量实际上包含在频率最低的波中：这些波是本项目的核心。惯性波是由风在海洋表面产生的，具有很高的能量，容易受到引起湍流和混合的不稳定性的影响。由于惯性波是海洋顶层以下垂直混合的主要来源，因此惯性波对于污染物的扩散和生物活动至关重要。也许更令人惊讶的是，它们在建立深海密度分层方面也至关重要。因此，它们对大规模的海洋环流有很大的影响，从而对地球的气候有很大的影响。因此，用于气候预测的数值模式必须考虑到惯性波的影响。然而，这是一个挑战。由于惯性波的尺度比海洋环流的典型尺度小得多，气候模型不可能完全描述（即，以解析）与波相关联的运动的细节。相反，这些模型必须代表大尺度的全球性波浪效应，并将这种效应与它们所描述的过程联系起来，如表面风和大尺度海流。这就是参数化方案的作用，参数化方案是气候模式中最重要（也是最微妙）的组成部分之一。为了准确和稳健，这些参数化方案必须基于对它们所代表的未解决现象的正确理解。该项目将建立对风产生的惯性波的理解。它将首先开发一个专门用于研究惯性波的新的数值模型。该模型针对惯性波进行了大量简化;由于这些简化，其计算成本比传统模型低得多。因此，它将为惯性波的研究提供一种独特的、高效的工具。它将以更昂贵的模型的结果和漂浮在海洋表面附近的漂流者所做的一系列测量为基准。然后将研究惯性波在海洋中的传播。将考虑三个具体方面：小的垂直尺度的电流的影响，散射和消散的底部地形附近的波，和直接的大尺度强迫引起的耗散惯性波。这将大大提高对惯性波动力学的理解，并为设计气候模型和区域海洋模型中实施的参数化方案铺平道路。

The combination of the ocean's density stratification and the earth's rotation results in the existence of waves, termed inertia-gravity waves, which propagate through the whole depth of the ocean and make a large contribution to its energy. Most of the energy of inertia-gravity waves is in fact contained in the waves with the lowest frequencies: these are the inertial waves at the centre of this project. Inertial waves, which are generated by wind at the ocean's surface, are highly energetic and susceptible to instabilities which induce turbulence and mixing. Because they are the primary source of vertical mixing below the immediate top layer of the ocean, inertial waves are crucially important for the dispersion of pollutants and for biological activity. More surprisingly perhaps, they are also crucial in establishing the density stratification of the deep ocean. As a result, they have a strong influence on the large-scale circulation of the ocean and thereby on the earth's climate. It is therefore very important that the numerical models that are used for climate predictions take into account the effect of inertial waves. This is challenging, however. Because the scales of the inertial waves are much smaller than the typical scales of the ocean's circulation, it is not possible for climate models to describe fully (i.e., to resolve) the details of the motion associated with the waves. Instead, the models must represent the large-scale, global effect of the waves and relate this effect to the processes which they describe well, such as the surface winds and large-scale currents. This is the role of parameterisation schemes, which are one of the most important (and delicate) components of climate models. To be accurate and robust, these parameterisation schemes must be based on a sound understanding of the unresolved phenomena they represent. This project will build this understanding for wind-generated inertial waves. It will start by the development of a new numerical model specifically dedicated to the study of inertial waves. This model makes a number of simplifications tailored to inertial waves; thanks to these simplifications, its computational cost is much lower than that of traditional models. It will therefore provide a unique, highly efficient tool for the study of inertial waves. It will be benchmarked against the results of more costly models and against a series of measurements made by drifters floating near the ocean's surface. The propagation of inertial waves through the ocean will then be examined. Three specific aspects will be considered: the influence of currents with small vertical scales, the scattering and dissipation of the waves near the bottom topography, and the direct large-scale forcing induced by dissipating inertial waves. This will lead to a greatly improved understanding of the dynamics of inertial waves and pave the way for the design of parameterisation schemes to be implemented in climate models and in regional ocean models.