Zonation

带状射流是一个知之甚少的过程的结果，通过该过程自发产生的雷诺应力破坏了空间均匀的β平面湍流的初始状态。 这种不稳定性的最终平衡导致了与湍流共存的成熟的纬向射流模式。 湍流的所有性质，特别是标量和位涡的输送，都被射流大大改变。 该项目将开发新的方法来定量分析射流形成的不稳定性和参数化这些流动中的传输。 主要的假设是，不稳定性是能量的转移，非本地波数，从强迫尺度直接到急流尺度。 初步结果支持这一假设，并建议负涡动粘度可能连接的动量通量平均剪切。 该提案的关键是理解和建模的非线性反馈饱和的不稳定性。 在物理海洋学中，有几种关于涡旋热量和标量通量参数化的建议。 在这一讨论中，由于假设横向或层向动量通量在大尺度上不重要，所以几乎忽略了这种过程。 令人信服的观测证据表明，纬向急流存在于海洋中，意味着这种近似的失败。 这一建议所解决的紧迫的海洋学问题是负粘性动量通量的起源，以及对示踪剂输运的影响。纬向流的动力学对海洋学、气象学、行星物理学和等离子体物理学具有重要意义。 湍流中结构的形成是一个引人注目的物理现象，由湍流雷诺应力驱动的带状流就是一个最重要的例子。 纬向气流饱和的机制以及纬向气流如何在热量和位涡通量的调节中定量出现的问题还没有得到很好的理解。 该项目将提供有物理根源的涡流动量通量参数化，可用于粗分辨率气候模式。 斯克里普斯海洋学研究所的一名研究生将接受理论问题表述、地球物理流体动力学、应用数学、分析和科学计算等领域的培训。

Zonal jets are the result of a poorly understood process via which spontaneously arising Reynolds stresses destroy an initial state of spatially homogeneous beta-plane turbulence. The ultimate equilibration of this instability results in a mature pattern of zonal jets, co-existing with turbulence. All properties of the turbulence, particularly the transport of scalars and potential vorticity, are substantially modified by the jets. This project will develop new approaches to quantitatively analyzing the jet-forming instability and parameterizing transport in these flows. The main hypothesis is that the instability is a transfer of energy, non-local in wave-number, from the forcing scale directly to the jet scale. Preliminary results are supportive of this hypothesis and suggest that negative eddy viscosity may connect the momentum fluxes to mean shear. Essential to the proposal is understanding and modeling the nonlinear feedbacks required to saturate the instability. In physical oceanography there are several proposals for the parameterization of eddy heat and scalar fluxes. Lateral or layerwise momentum fluxes have been almost ignored in this discussion, with the assumption that this processes is unimportant on large scales. Compelling observational evidence that zonal jets exist in the ocean, imply a failure of this approximation. The pressing oceanographic problem addressed by this proposal is the origin of negative viscosity momentum fluxes, and implications for the transport of tracers.The dynamics of zonal flows has important implications for oceanography, meteorology, planetary physics and plasma physics. Structure formation in the midst of a turbulent flow is a striking physical phenomenon, and zonal flows driven by turbulent Reynolds stresses are a foremost example. The mechanism of zonal flow saturation and the question of how, quantitatively, zonal flows figure in the regulation of heat and potential vorticity fluxes are not well understood. The project will provide physically-rooted parameterizations of eddy momentum fluxes, which might be used in coarse resolution climate models. A graduate student at Scripps Institution of Oceanography will receive training in the areas of theoretical problem formulation, geophysical fluid dynamics, applied mathematics, analysis and scientific computation.