Transport in Baroclinic Flows

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。示踪剂在斜压流中的传输将被调查，使用修改后的拉格朗日平均方法的角度中村。该方法已被开发和应用到目前为止的情况下，一个纯粹的二维级联的示踪剂方差最终耗散的小规模扩散。在大多数大气和海洋感兴趣的流动中，叶栅是三维的：即使平衡流动是分层二维的，它们也有斜压切变。因此，示踪剂方差下降到精细水平尺度的级联伴随着垂直尺度的级联，在实践中，垂直尺度要精细得多。因此，在几乎所有这些情况下，阻止连锁反应的是垂直扩散，而不是水平扩散。这项研究的核心目的是评估这对我们理解大规模运输的影响。理论表明，人们仍然可以定义准水平输运的有效扩散率，用倾斜示踪剂等值线的等效面积代替二维情况的等效长度。此外，该理论还提供了净垂直（非绝热）输送的表达式，尽管对该表达式的解释不是很清楚。一系列平流层和海洋流输运数值模拟的结果将被用来验证、评估和促进理论预测的进一步发展，这项研究将解决目前大气和海洋平衡流输运二维理论的一个明显缺陷，并将导致对斜压流中混沌输运的更深入理解。从理论和概念的角度来看，更广泛的影响包括将结果广泛应用于地球物理流体动力学，更实际地说，允许对大气和海洋中的水平和垂直迁移率进行定量评估。将培养一名研究生。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The transport of tracers in baroclinic flows will be investigated, using the perspective of the modified Lagrangian mean approach of Nakamura. The approach has been developed and applied thus far to the case of a purely two-dimensional cascade of tracer variance to ultimate dissipation by small-scale diffusion. In most flows of atmospheric and oceanic interest, the cascade is three-dimensional: even though the balanced flows are layerwise two-dimensional, they have baroclinic shear. In consequence, the cascade of tracer variance down to fine horizontal scales is accompanied by a cascade of vertical scales which, in practice, are much finer. Consequently, in almost all such circumstances it is vertical, not horizontal, diffusion that arrests the cascade. It is the core intention of this research to assess the implications of this for our understanding of large-scale transport. Theory suggests one can still define an effective diffusivity for quasi-horizontal transport, with the equivalent area of the tilted tracer contours replacing the .equivalent length of the two-dimensional case. Further, the theory also provides an expression for the net vertical (diabatic) transport, though the interpretation of this expression is not so clear. Output from a series of numerical simulations of transport in stratospheric and oceanic flows will be used to demonstrate, to assess, and to facilitate further development of, the theoretical predictions.This study will address an obvious shortcoming of current two-dimensional theories of transport by balanced flows in the atmosphere and ocean and will lead to a deeper understanding of chaotic transport in baroclinic flows. The broader impacts include, from a theoretical and conceptual viewpoint, wide application of the results in geophysical fluid dynamics and, more practically, permit the quantitative assessment of horizontal and vertical transport rates in the atmosphere and ocean. A graduate student will be trained.