Quantifying Transport and Mixing in the Stratosphere and Upper Troposphere

该研究项目将有助于提高对平流层极涡破裂期间非线性过程的动力学和可预测性的理解，这是冬末春初极端寒冷爆发事件的原因。 这项研究还可能揭示在气候变化中负责输送和混合的过程。 在对流层上层，这与大气河流、阻塞和其他类型的极端天气有关，这些极端天气具有重要的社会影响。 该研究项目的成果预计将对广泛的流体流动问题产生广泛影响，并在动力系统理论与大气和海洋流体应用之间产生更多对话。加州大学洛杉矶分校的一名研究生将接受观测数据分析和理想化综合大气模型使用方面的培训。 几名本科生将接受大气环流数据分析的培训。热带外大气的特点是西风绕极流，平流层有极涡，对流层上层有副热带急流。 平流层极涡和对流层急流的变化对这些地区的动力学、化学和可预测性至关重要。 平流层行星尺度Rossby波振幅的增加中断了西风绕极气流，导致更强的暖空气质量输送到极地平流层，并导致那里突然变暖。在平流层突然变暖事件期间，臭氧的更强传输有助于防止极地地区在黑暗的冬季期间臭氧的持续损失。 同样，对流层上部西风气流的阻塞也会影响能量、动量和水汽的输送。对于大振幅波存在下的非线性流动性质仍然缺乏了解，这限制了我们预测这些事件的能力。 本项目的目标是从动力系统的观点结合大气中的输送和混合理论，获得关于西风气流中拉格朗日输送（跟随气团运动）的基本过程的新知识。 更具体地说，平流层变暖事件将以拉格朗日描述符为特征，拉格朗日描述符是一种源自动力系统的度量，在平流层-对流层耦合的观测和理想化模型中。 观测到的模式将与综合化学气候模式中的输送和混合以及不同时间尺度卫星观测中的化学成分进行比较。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.