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arXiv 1503.06457physics.plasm-phnlin.PSphysics.ao-ph
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流体和等离子体中的带状流和Turbulence

Zonal Flows and Turbulence in Fluids and Plasmas

Jeffrey B. Parker

摘要:

在地球物理学和等离子体背景下,众所周知纬向流是由湍流引起的。我们阐明了从统计均匀湍流无纬向流统计非均匀湍流定常纬向流的过渡。从长谷川-Mima方程出发,我们采用了拟线性近似和统计平均,它保留了大量的定性行为的完整系统。在由此产生的框架内被称为CE 2,我们扩展最近的理解的破坏性的“zonostrophic不稳定性”。纬向不稳定性可以非常普遍地理解为某些湍流背景谱对纬向对称相干模的不稳定性。作为一种特殊情况,背景光谱可以仅由单一模式组成。我们发现,在这种情况下,从CE 2形式主义的纬向不稳定的色散关系,正好减少到广义调制不稳定的四模截断。然后,我们表明,纬向流构成斑图形成在湍流浴。纬转不稳定性是模式形成系统的I型$_s$不稳定性的一个例子。对称性破缺就是统计均匀性。在分叉点附近,CE 2的慢动力学由一个著名的振幅方程,即真实的Ginzburg-Landau方程控制。这个振幅方程的重要特征是多重的,因此也是CE 2系统的重要特征。首先,纬向流波长不是唯一的。在一个理想化的无限系统中,存在一个连续的带状流波长带,允许非线性平衡。其次,在这些波长中,只有那些在较小子带内的波长是稳定的。不稳定的波长必须演化到稳定的波长;这个过程表现为合并射流。这些行为…

英文摘要:

In geophysical and plasma contexts, zonal flows are well known to arise out of turbulence. We elucidate the transition from statistically homogeneous turbulence without zonal flows to statistically inhomogeneous turbulence with steady zonal flows. Starting from the Hasegawa--Mima equation, we employ both the quasilinear approximation and a statistical average, which retains a great deal of the qualitative behavior of the full system. Within the resulting framework known as CE2, we extend recent understanding of the symmetry-breaking `zonostrophic instability'. Zonostrophic instability can be understood in a very general way as the instability of some turbulent background spectrum to a zonally symmetric coherent mode. As a special case, the background spectrum can consist of only a single mode. We find that in this case the dispersion relation of zonostrophic instability from the CE2 formalism reduces exactly to that of the 4-mode truncation of generalized modulational instability. We then show that zonal flows constitute pattern formation amid a turbulent bath. Zonostrophic instability is an example of a Type I$_s$ instability of pattern-forming systems. The broken symmetry is statistical homogeneity. Near the bifurcation point, the slow dynamics of CE2 are governed by a well-known amplitude equation, the real Ginzburg-Landau equation. The important features of this amplitude equation, and therefore of the CE2 system, are multiple. First, the zonal flow wavelength is not unique. In an idealized, infinite system, there is a continuous band of zonal flow wavelengths that allow a nonlinear equilibrium. Second, of these wavelengths, only those within a smaller subband are stable. Unstable wavelengths must evolve to reach a stable wavelength; this process manifests as merging jets. These behaviors ...

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