Eddy Mean Flow Interactions in the Kuroshio Extension

摘要黑潮扩展系统研究（KESS）提供了一套前所未有的观测数据，非常适合研究急流、涡旋变率及其相互作用。本研究的目的是利用KESS和辅助观测资料来表征黑潮扩展（KE）中的涡流-平均流相互作用，研究与WBC射流扩展系统相关的理想化配置中的涡流-平均流相互作用，并最终检验这些理想化研究得出的理论认识与海洋系统的相关性。这项工作将对局部强迫的涡流驱动再循环环流的机制产生新的见解，这种再循环环流的强度与在KE和墨西哥湾流中观察到的深层再循环速度一致，并支持与这些喷射系统相关的再循环至少部分是由涡流驱动的假设。此外，在非线性动力学的影响下，是什么决定了平均射流及其再循环的特性，也将获得新的见解。与海洋的大多数其他区域相比，沿WBC射流平均路径的涡旋能量要大几个数量级，我们预计涡旋变率在这些系统的动力学中起着重要作用。KESS数据集提供了一个独特的机会来扩展我们目前对这一角色的性质和重要性的理解，特别是，使我们能够理解不稳定射流中涡平均流相互作用的理论如何应用于实际的海洋。这项研究的一个预期结果是提高对控制WBC射流侧面再循环环流强度和结构的过程的理解。再循环环流从根本上改变了急流的动力结构，并显著增加了这些流的净输送。它们也是亚热带模态水形成的重要场所。这项工作将测试这些再循环区是涡流驱动的假设，并试图确定在这一过程中正压和斜压不稳定的相对重要性。这项工作的结果有望提高对WBC射流的理解，因为这些系统中的涡流平均流相互作用可能对它们的整体动力学至关重要。wbc是全球热输送的重要组成部分之一，因此对全球气候具有调节作用。因此，在此吸取的经验教训将对评估气候研究所需的实际海洋环流模式，以及在东太平洋区域为最终实现CLIVAR目标设计高效和有效的监测战略具有重要的应用价值。这项工作可能会对海洋建模产生影响。它可以使人们更好地理解在这些系统中解决各种涡旋过程的影响和重要性。所寻求的对动力学机制的见解可能为未解决的涡流的影响提供合适的参数化。

ABSTRACTThis study was motivated by the Kuroshio Extension System Study (KESS), which provides an unprecedented suite of observations uniquely suited to study the jet, its eddy variability, and their interactions. The goals of the study are to characterize eddy-mean flow interactions in the Kuroshio Extension (KE) from the KESS and supporting observations, to examine eddy-mean flow interactions in idealized configurations relevant to WBC jet extension systems, and finally to test the relevance of the theoretical understanding derived from these idealized studies to the oceanic system. This work WILL result in new insights into a mechanism by which eddies from a localized forcing can drive recirculation gyres of a strength consistent with the deep recirculation velocities observed in the KE and Gulf Stream, as well as support for the hypothesis that the recirculation associated with these jet systems are, at least partially, eddy-driven. In addition, new insights will be gained into what may determine the properties of the mean jet and its recirculation as they evolve downstream as a consequence of the nonlinear dynamics. Eddy energies are orders of magnitude larger along the mean paths of WBC jets compared to most other regions of the ocean and we expect eddy variability to play an important role in the dynamics of these systems. The KESS data set provides a unique opportunity to extend our present understanding of the nature and importance of this role, in particular, allowing us to understand how theories about eddy-mean flow interaction in unstable jets apply to the actual ocean. One anticipated result of this research is improved understanding of the processes that govern the strength and structure of the recirculation gyres that flank WBC jets. Recirculation gyres fundamentally alter the dynamical structure of the jet and add significantly to the net transport of these currents. They also are important as the sites of subtropical mode water formation. This work will test the hypothesis that these recirculation zones are eddy-driven and seek to determine the relative importance of barotropic and baroclinic instability in this process.Results from this work promise an improved understanding of WBC jets, as eddy-mean flow interactions in these systems are likely critical to their overall dynamics. WBCs are one of the foremost components in global heat transport and thus in regulating the global climate. As such, the lessons learned here will have important application to the evaluation of realistic ocean general circulation models required for climate studies, and also to the design of an efficient and effective monitoring strategy in the KE region for eventual achievement of CLIVAR goals. This work likely has implications for ocean modeling. It may lead to an improved understanding of the impact and importance of having various eddy processes resolved in these systems. The insights into the dynamical mechanisms that are sought may suggest suitable parameterizations for the effects of unresolved eddies.