Stochastic Dynamics of Sudden Stratospheric Warmings

大多数时候，北半球极地帽上平流层的冬季环流，或平流层极地涡旋，与极点近似对称，但偶尔它会转变成一种戏剧性的波浪状状态，在这种状态下，平流层的温度在不到一周的时间里上升了40摄氏度。这些转变被称为平流层突然变暖（SSWs），它们构成极地平流层变率的主要形式。这个研究项目将研究小尺度重力波的随机变率（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转换的思想，这种转换已知发生在简单的动力系统中，其中两个稳定的平衡状态是可能的。研究将以不同复杂程度的模型分层进行，从已知有两种稳定状态的三参数系统开始，逐步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。这项工作将对研究生的教育产生更广泛的影响。研究结果将有助于我们了解ssw，这些ssw已被证明对地面天气有重要影响，并可能对改善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.