Quantifying Transport and Mixing in the Stratosphere and Upper Troposphere

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This research project will help improve the understanding of the dynamics and predictability of nonlinear processes during a breakdown of polar vortex in the stratosphere, responsible for extreme cold outbreak events in the late winter and early spring. This study may also shed light on processes responsible for transport and mixing across the edge of polar vortex in a changing climate. In the upper troposphere, this is relevant for atmospheric rivers, blocking, and other type of extreme weather that has important societal impacts. The outcome of the research project is expected to have broad implications across a very wide range of fluid flow problems and generate more dialogues between the theory of dynamical systems and applications to atmospheric and oceanic fluids. One graduate student at UCLA will be trained in analysis of observational data and the use of idealized and comprehensive models of the atmosphere. Several undergraduates will be trained in data analysis of atmospheric circulation.The extratropical atmosphere is characterized by the westerly circumpolar flow, with the polar vortex in the stratosphere and the subtropical jet stream in the upper troposphere. Variations in the stratospheric polar vortex and tropospheric jet stream are critical for the dynamics, chemistry, and predictability of these regions. Increases in the amplitude of planetary-scale Rossby waves in the stratosphere interrupt the westerly circumpolar flow, resulting a stronger transport of warm air mass into the polar stratosphere and leading to a sudden warming there. The stronger transport of ozone during a stratospheric sudden warming event helps prevent a continuous loss of ozone over the polar regions during dark winter there. Similarly, the blocked westerly flow in the upper troposphere can impact the transport of energy, momentum as well as water vapor. There is still a lack of understanding about the nonlinear nature of the flow in the presence of large amplitude waves, which limits our ability to predict these events. The objective of this project is to gain new knowledge on the fundamental processes at work for the Lagrangian transport (following the motion of air parcel) in the westerly flow from the dynamical systems point of view in conjunction with the theory of transport and mixing in the atmosphere. More specially, stratospheric warming events will be characterized by the Lagrangian descriptor, a metric stemmed from the dynamical systems, in observations and idealized models of stratosphere-troposphere coupling. The observed patterns will be compared with transport and mixing in a comprehensive chemistry-climate model and chemical compositions in satellite observations at different time scales.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.