Abstract We investigate the stability of a composite cyclone representative of Arabian Sea eddies using a high resolution primitive equation model. We observe that the eddy is unstable with respect to a mixed barotropic/baroclinic instability, leading to the growth of an azimuthal mode 2 perturbation. The latter deforms the eddy, which eventually evolves into a tripole after about 4 months of simulation. The presence of a critical level for the most unstable mode generates sharp fronts in the surface mixed layer where the Rossby number is large. These fronts then become unstable, and this generates submesoscale cyclones and filaments. Near these fronts, diapycnal mixing occurs, causing the potential vorticity to change sign locally, and symmetric instability to develop in the core of the cyclonic eddy. Despite the instabilities, the eddy is not destroyed and remains a large-scale coherent structure for the last 6 months of the simulation. Looking at Sea Surface Height only, the composite eddy evolves little, and fairly represents the eddy observed in the altimetry which can live for several months. The study of this simulation thus illustrates the numerous kinds of instabilities which may occur in large cyclonic eddies but cannot be captured directly by altimetric data.

中文翻译：

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大型现实气旋涡旋稳定性研究

摘要 我们使用高分辨率原始方程模型研究了代表阿拉伯海涡流的复合气旋的稳定性。我们观察到涡流对于混合的正压/斜压不稳定性是不稳定的，导致方位角模式 2 扰动的增长。后者使涡流变形，经过大约 4 个月的模拟，最终演变为三极。最不稳定模式的临界水平的存在会在罗斯比数很大的表面混合层中产生尖锐的锋面。然后这些锋面变得不稳定，从而产生亚中尺度气旋和细丝。在这些锋面附近，发生了穿心混合，导致潜在涡量局部改变符号，并且在气旋涡旋的核心发展对称不稳定性。尽管不稳定，在模拟的最后 6 个月，涡流没有被破坏，并且仍然是一个大规模的连贯结构。仅从海面高度来看，复合涡旋几乎没有演变，并且相当地代表了在高度计中观察到的可以持续数月的涡旋。因此，对这种模拟的研究说明了在大型气旋涡流中可能发生但不能直接由高度数据捕获的多种不稳定性。