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Dynamic Transitions and Baroclinic Instability for 3D Continuously Stratified Boussinesq Flows

机译:三维连续动态转换与斜压不稳定性   分层Boussinesq流动

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摘要

The main objective of this article is to study the nonlinear stability anddynamic transitions of the basic (zonal) shear flows for the three-dimensionalcontinuously stratified rotating Boussinesq model. The model equations arefundamental equations in geophysical fluid dynamics, and dynamics associatedwith their basic zonal shear flows play a crucial role in understanding manyimportant geophysical fluid dynamical processes, such as the meridionaloverturning oceanic circulation and the geophysical baroclinic instability. Inthis paper, first we derive a threshold for the energy stability of the basicshear flow, and obtain a criteria for nonlinear stability in terms of thecritical horizontal wavenumbers and the system parameters such as the Froudenumber, the Rossby number, the Prandtl number and the strength of the shearflow. Next we demonstrate that the system always undergoes a dynamic transitionfrom the basic shear flow to either a spatiotemporal oscillatory pattern orcircle of steady states, as the shear strength $\Lambda$ of the basic flowcrosses a critical threshold $\Lambda_c$. Also we show that the dynamictransition can be either continuous or catastrophic, and is dictated by thesign of a transition parameter $A$, fully characterizing the nonlinearinteractions of different modes. A systematic numerical method is carried outto explore transition in different flow parameter regimes. We find that thesystem admits only critical eigenmodes with horizontal wave indices $(0,m_y)$.Such modes, horizontally have the pattern consisting of $m_y$-rolls alignedwith the x-axis. Furthermore, numerically we encountered continuous transitionsto multiple steady states, continuous and catastrophic transitions tospatiotemporal oscillations.
机译:本文的主要目的是研究三维连续分层旋转Boussinesq模型的基本(区域)剪切流的非线性稳定性和动态过渡。模型方程是地球物理流体动力学中的基本方程,与它们的基本纬向剪切流有关的动力学在理解许多重要的地球物理流体动力学过程(例如经向翻转海洋环流和地球物理斜压不稳定性)中起着至关重要的作用。在本文中,首先我们推导了基本剪切流的能量稳定性阈值,并根据临界水平波数和系统参数(如Froudenumber,Rossby数,Prandtl数和强度)获得了非线性稳定性的判据。剪切流。接下来,我们证明系统始终经历从基本剪切​​流到时空振荡模式或稳态圆的动态过渡,因为基本流的剪切强度$ \ Lambda $越过临界阈值$ \ Lambda_c $。我们还表明,动态过渡可以是连续的,也可以是灾难性的,并且由过渡参数$ A $的符号所决定,充分表征了不同模式的非线性相互作用。进行了系统的数值研究,探讨了不同流动参数状态下的过渡过程。我们发现系统仅允许使用水平波指数为$(0,m_y)$的临界本征模,这种模式在水平方向上具有由与x轴对齐的$ m_y $卷组成的模式。此外,在数值上,我们遇到了从连续过渡到多个稳态,从连续和灾难性过渡到时空振荡的问题。

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