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

*大到中尺度的海洋环流可以看作是运动的近地转和近惯性分量的叠加。缓慢演化的地转场包含了大约90%的动能，而较快的近惯性场(接近科里奥利频率的频率)占了大部分。这种差异在很大程度上是由于这两类流动中的能量在地球物理湍流中表现方式的根本不同。近惯性能量很容易转移到耗散尺度，而地转能量则不容易。因此，模拟地转环流涉及到对能量耗散机制的假设。一种常见的假设是，地转能量通过与底部边界层的相互作用而被移除。然而，由于海底是不可到达的，底部阻力系数在很大程度上是通过调整练习来确定的。这导致了寻找地转能量消散的替代途径。特别是，地转到近惯性的能量转移与近惯性能量的前向级联被提出。许多早期的工作都集中在通过其他(地转)平衡流自发地产生不平衡运动。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式的外部强迫的作用。许多关于这种刺激性平衡丧失的工作i)集中在相对较小的范围内，ii)使用不同的诊断方法来定义或模拟平衡。这里提出的工作主要集中在海洋中尺度(10-100公里)，并使用补充诊断来检查强迫近惯性运动对平衡流动的影响。该方法允许使用不同复杂性的理论和模型的一系列项目。它将为本科生、硕士和博士水平的HQP提供在海洋环流理论和模型方面获得坚实基础的机会。由于所讨论的一些问题也与大气相对应，这个研究框架也让我能够吸引学生，他们的先天兴趣可能更集中在大气应用上，而不是海洋应用。毕业时，学生们将扎根于地球物理流体动力学，并了解他们的工作如何适应物理海洋学、气象学和气候动力学等更广泛的背景。**

***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. **