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。利用Nakamura的修正拉格朗日平均方法，研究了斜压流中示踪剂的输运。到目前为止，该方法已经发展并应用于纯二维示踪剂方差级联的情况下，最终耗散的小尺度扩散。在大多数与大气和海洋有关的气流中，叶栅是三维的；尽管平衡气流在层上是二维的，但它们具有斜压切变。因此，示踪剂方差的级联下降到精细的水平尺度，伴随着垂直尺度的级联，在实践中，更精细。因此，在几乎所有这样的情况下，阻止级联的是垂直扩散，而不是水平扩散。本研究的核心意图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系数，用倾斜示踪线的等效面积代替。二维情况下的等效长度。此外，该理论还提供了净垂直（绝热）输运的表达式，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动中运输的数值模拟的结果将用于证明、评估和促进理论预测的进一步发展。该研究将解决目前二维大气和海洋平衡流输运理论的一个明显缺陷，并将对斜压流中的混沌输运有更深入的认识。从理论和概念的观点来看，更广泛的影响包括广泛应用地球物理流体动力学的结果，更实际地说，允许对大气和海洋中的水平和垂直输送率进行定量评估。研究生将接受培训。

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.