Spectrally resolving the ocean’s Lorenz energy cycle

中尺度涡旋与空间尺度约。5至200公里是海洋环流的一个重要特征。它们的产生机制和对输送和混合的影响是众所周知的，并且从小尺度到大尺度的反向能量级联通量涡动动能（EKE）似乎是海洋动力学的一个强大的观测特征。它遵循传统的模式，从较小尺度的涡流产生到较大尺度的耗散的逆涡流能量级联。 这个范例的问题是，没有多少过程可以合理地解释大尺度的耗散（例如，海洋模型中的摩擦有利于小尺度）。然而，这种传统的范式最近受到了挑战，光谱解决的涡动能量生产条款在高分辨率的海洋模式：我们和其他作者发现了一个尺度依赖的迹象，在中高纬度的EKE生产条款。在那里，EKE在大尺度上被转换回势能，这几乎平衡了逆能量级联。 由于一个前向级联到较小尺度的能量水库饲料EKE，因此可以预期在较高的纬度，它建议频谱解决所有其他条款的所谓的洛伦兹能量循环，以了解能量级联的洛伦兹能量循环，并解决我们缺少的理解的涡流能量路径耗散。两个问题需要解决这一奋进：平均在恒定的深度，而不是等密度平均，和可用的势能的定义。由于这两个问题是很难解决的现实海洋模型，我们建议这样做，而不是在理想化的海洋模型，在那里的问题可以很容易地解决，然后我们回到现实的海洋模型。我们的基本假设是，这两个问题将不会改变定性的结果，这将提供我们的新的解释光谱解决洛伦兹能量循环在现实的模型的信心。本文的研究结果将为研究不同纬度海洋中尺度涡动耗散和涡动能量循环提供新的视角。

Mesoscale eddies with spatial scales of ca. 5 to 200 km are an important feature of the ocean circulation. Their generation mechanism and effects on transport and mixing are well known, and an inverse energy cascade fluxing eddy kinetic energy (EKE) from small to larger scales appears to be a robust observed feature of ocean dynamics. It follows the traditional paradigm of an inverse eddy energy cascade from the smaller scales of eddy production to dissipation at larger scales. Problematic in this paradigm is that not many processes are plausible to account for dissipation at large scales (e.g. friction in ocean models favors small scales). However, this traditional paradigm has been challenged recently by spectrally resolving the eddy energy production terms in high-resolution ocean models: We and other authors found a scale-dependent sign of the EKE production term at mid- to high latitudes. There, EKE is transferred back to potential energy at large scales, which nearly balances the inverse energy cascade. Since a forward cascade to smaller scales in the energy reservoirs feeding EKE can therefore be expected at higher latitudes, it is proposed to spectrally resolve all other terms of the so-called Lorenz energy cycle to understand the energy cascades in the Lorenz energy cycle, and to resolve our missing understanding of the eddy energy route to dissipation. Two issues need to be resolved for this endeavor: averaging at constant depth instead of isopycnal averaging, and the definition of available potential energy. Since both issues are difficult to resolve in realistic ocean models, we propose to do so in idealized ocean models instead, where the issues can be readily resolved, before we return to the realistic ocean model. Our underlying hypothesis is that both issues will not qualitatively change results, which will provide confidence of our novel interpretation of the spectrally resolved Lorenz energy cycle in the realistic model. The result of our work will be a new view on mesoscale eddy dissipation and eddy energy cycle at different latitudes of the ocean.