Interaction between near-inertial and geostrophic flow in idealized ocean circulation models

大尺度到中等尺度的海洋环流可以被认为是近地转和近惯性运动分量的叠加。的 缓慢演变的地转场包含大约90%的动能，而较快的近惯性场（频率接近科里奥利频率） 占其余的大部分。这一差异主要归因于 这两类能源的方式有着根本的不同， 流动表现为地球物理湍流。近惯性能量很容易转移到耗散尺度，而地转能量则不然。建模 因此，地转环流涉及对能量耗散机制的假设。一个常见的假设是，地转能量是 通过与底部边界层的相互作用而被去除。因为大海 底部是不可接近的，然而，底部阻力系数在很大程度上是 通过调音练习确定。 这导致了寻找其他途径来消散地转能量。特别是， 已经提出了与近惯性能量的前向级联耦合的地转能量到近惯性能量的传递。沿着这条路线，沿着许多早期的工作都集中在不平衡运动的自发产生上，这种运动是由另外的（地转的）平衡流引起的。然而，这种平衡的丧失是微弱的， 最近的工作强调了近惯性模态的外力作用。大部分关于这种刺激失去平衡的工作i）集中在相对较小的尺度上，ii）使用不同的诊断来定义或建模平衡。这里提出的工作主要集中在海洋中尺度（10-100公里），并使用互补的诊断，以检查强迫近惯性运动的平衡流的效果。该方法允许使用不同复杂性的理论和模型的一系列项目。它将为HQP在本科生，硕士和博士水平，以获得在海洋环流的理论和建模的坚实基础的机会。由于一些问题的处理也有大气对应部分，这个研究框架也使我能够吸引学生的先验兴趣可能更集中在大气，而不是海洋的应用。 学生将退出我的计划，坚定地扎根于地球物理流体动力学，并赞赏他们的工作如何融入物理海洋学，气象学和气候动力学的更广泛的背景。

Ocean circulation at large to intermediate scales can be thought of as a superposition of nearly-geostrophic and near-inertial components of motion. The slowly evolving geostrophic fields contains about 90% of the kinetic energy while the faster near-inertial field (frequencies near the Coriolis frequency) accounts for most of the remainder. This difference is attributable in large part to a fundamental difference in the way energy in these two classes of flow behave in geophysical turbulence. Near-inertial energy is readily transferred to dissipation scales, whereas geostrophic energy is not. Modelling the geostrophic circulation thus involves making assumptions regarding energy dissipation mechanism. A common assumption is that geostrophic energy is removed through interaction with the bottom boundary layer. Because the sea floor is inaccessible, however, bottom drag coefficients are in large part determined via a tuning exercise. This has led to the search for alternative routes to dissipation for geostrophic energy. In particular, geostrophic-to-near-inertial energy transfers coupled with a forward cascade of near-inertial energy has been proposed. Much of the earlier work along these lines has focused on spontaneous generation of unbalanced motion by an otherwise (geostrophically) balanced flow. This loss of balance, however, is weak and more recent work emphasizes the role of external forcing of the near-inertial modes. Much of the work on this stimulated loss of balance i) focusses on relatively small scales and ii) uses different diagnostics to define or model balance. The work proposed here focuses primarily on the ocean mesoscale (10-100 km) and uses complementary diagnostics to examine the effect of forced near-inertial motion on the balanced flow. The approach allows for a range of projects using theory and models of different complexity. It will provide opportunities for HQP at the undergraduate, MSc and, PhD levels to gain a solid foundation in the theory and modelling of ocean circulation. Because some of the problems treated also have atmospheric counter-parts, this research framework also allows me to attract students whose a priori interest may be more centred on atmospheric rather than oceanic applications. Students will exit my program with a firm rooting in geophysical fluid dynamics and an appreciation of how their work fits into the broader contexts of physical oceanongraphy, meteorology, and climate dynamics.