Successive bifurcations in a simple model of atmospheric zonal-flow vacillation.
Successive bifurcations in a simple model of atmospheric zonal-flow vacillation.
复制标题
大气纬向流振荡的简单模型中的连续分岔。
作者：
Seongjoon Koo;M. Ghil
南半球气流的低频变率主要受中纬度东向急流的纬度和强度在其气候平均状态附近的不规则变化所控制。这种现象被称为大气纬向流摆动，其特征在于纬向流存在两种持续状态（即，东西向的）急流和它们之间的不规则过渡。平均流和波浪之间的非线性相互作用在这种波动的动力学中起着关键作用。在本研究中，我们发展了一个低阶的，确定性模式的非线性动力学的大气纬向流摆动。多重平衡出现在这个模式的纬向平均气流中，也就是说，出现在沿沿着给定纬度圈平均的纵向气流中。这些平衡与南半球观测中发现的两种持续流态有很大的相似之处。这两种平衡状态是由波浪对表面阻力的作用力维持的，正如观测结果所示。随着模型耗散参数的减小，连续分叉到周期性和混沌的带状平均流态。(c)2002年美国物理学会。
Low-frequency variability of the atmospheric flow in the Southern Hemisphere is dominated by irregular changes in the latitude and intensity of the mid-latitude eastward jet about its climatological mean state. This phenomenon, known as atmospheric zonal-flow vacillation, is characterized by the existence of two persistent states of the zonal (i.e., east-west oriented) jet and irregular transitions between them. Nonlinear interactions between the mean flow and the waves play a key role in the dynamics of this vacillation. In the present study, we develop a low-order, deterministic model for the nonlinear dynamics of atmospheric zonal-flow vacillation. Multiple equilibria arise in this model's zonal-mean flow, that is, in the longitudinal flow averaged along a given latitude circle. These equilibria bear a strong resemblance to the two persistent flow regimes found in Southern Hemisphere observations. The two equilibrium states are maintained by wave forcing against surface drag, as in the observations. Successive bifurcations to periodic and chaotic zonal-mean flow regimes occur as the model's dissipation parameter is reduced. (c) 2002 American Institute of Physics.