Stochastic Dynamics of Sudden Stratospheric Warmings

在大多数情况下，北半球极冠或平流层极涡上的平流层冬季环流围绕极点大致对称，但偶尔会转变为戏剧性的波状状态，在不到一周的时间里，平流层温度上升多达40摄氏度。这些转变被称为平流层突然变暖(SSW)，它们构成了极地平流层变化的主要形式。这项研究项目将审查小尺度重力波的随机变化(即浮力振荡)在多大程度上是产生SSW的一个重要因素。这项工作是基于噪声激活跃迁的思想，众所周知，这种跃迁发生在简单的动力系统中，在这个系统中可能有两个稳定的平衡态。这项研究将以不同复杂程度的模型层级进行，从已知有两个稳定状态的三参数系统开始，发展到具有平流层极地涡旋流动的完整三维表示的全球大气模型。这项工作将产生更广泛的影响，有助于研究生的教育。研究结果将有助于我们对SSW的理解，SSW已被证明对地面天气有影响，并可能对改进天气和气候模式有价值。

Most of the time, the winter circulation of the stratosphere over the Northern Hemisphere polar cap, or the stratospheric polar vortex, is approximately symmetric about the pole, but occasionally it transitions to a dramatically wave-like state, in which stratospheric temperatures rise by as much as 40 Celsius degrees in less than a week. These transitions are termed sudden stratospheric warmings (SSWs), and they constitute the dominant form of variability in the polar stratosphere. This research project will examine the extent to which the stochastic variability of small-scale gravity waves (i.e. buoyancy oscillations) are an important factor in producing SSWs. The work is based on the idea of noise-activated transitions which are known to occur in simple dynamical systems in which two stable equilibrium sates are possible. The research will be conducted with a hierarchy of models of differing complexity, starting from a three-parameter system which is known to have two stable states and progressing to a global atmospheric model with a full three-dimensional representation of the flow in the stratospheric polar vortex.The work will have broader impacts by contributing to the education of a graduate student. Results of the research will contribute to our understanding of SSWs, which have been shown to be consequential for surface weather, and may be of value for improving weather and climate models.