Stochastic Dynamics of Sudden Stratospheric Warmings

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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.