Invariant-tori-like Lagrangian coherent structures in geophysical flows.
Invariant-tori-like Lagrangian coherent structures in geophysical flows.
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DOI：
10.1063/1.3271342
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发表时间：
2010-01
期刊：
影响因子：
2.9
通讯作者：
F. Beron-Vera;M. J. Olascoaga;Michael G. Brown;H. Koçak;I. Rypina
中科院分区：
文献类型：
--
作者：
F. Beron-Vera;M. J. Olascoaga;Michael G. Brown;H. Koçak;I. Rypina
拉格朗日相干结构（Lagrangian coherent structure，LCS）一词通常用来描述数值检测到的结构，其性质类似于双曲轨道的稳定和不稳定流形。后一种结构是不变曲线，即，作为传输屏障的流体的材料曲线。在本文中，我们使用LCS来描述一种不同类型的结构，其性质类似于某些类别的二维不可压缩流的不变环面。像稳定和不稳定流形一样，不变环面是作为传输障碍的不变曲线。然而，传统的LCS和不变环面类LCS之间存在许多差异。这些差异进行了讨论，强调数值技术，可用于确定不变环面样LCS。这种类型的结构经常出现在地球物理流中，其中存在纬向喷流。不变环面状LCS的一个主要例子是在南半球冬季和早春，在地球平流层中下部的极地夜间急流核心附近的传输障碍;这是将臭氧消耗的空气困在臭氧洞内的障碍。这个例子是研究使用一个简单的解析规定的流量和速度场产生的地球大气环流模型。
The term "Lagrangian coherent structure" (LCS) is normally used to describe numerically detected structures whose properties are similar to those of stable and unstable manifolds of hyperbolic trajectories. The latter structures are invariant curves, i.e., material curves of fluid that serve as transport barriers. In this paper we use the term LCS to describe a different type of structure whose properties are similar to those of invariant tori in certain classes of two-dimensional incompressible flows. Like stable and unstable manifolds, invariant tori are invariant curves that serve as transport barriers. There are many differences, however, between traditional LCSs and invariant-tori-like LCSs. These differences are discussed with an emphasis on numerical techniques that can be used to identify invariant-tori-like LCSs. Structures of this type are often present in geophysical flows where zonal jets are present. A prime example of an invariant-torus-like LCS is the transport barrier near the core of the polar night jet in the Earth's lower and middle stratospheres in the austral winter and early spring; this is the barrier that traps ozone-depleted air inside the ozone hole. This example is investigated using both a simple analytically prescribed flow and a velocity field produced by a general circulation model of the Earth's atmosphere.