Variability of Midlatitude Transport and Mixing In a Warmer World

美国西部的空气质量不仅取决于当地的排放，还取决于来自该区域以外的污染物的输送，即来自跨越太平洋的亚洲排放的污染物，以及将自然产生的富臭氧空气带到地面的平流层入侵事件。对政策制定者来说，量化大规模大气输送对当今空气质量的贡献至关重要，因为一个地区符合当前空气质量标准的能力在一定程度上是背景气象条件的函数。此外，下个世纪温室气体浓度的增加预计将推动中纬度环流的巨大变化，但这些变化对污染物输送的影响还没有被很好地了解。本项目的目标是(1)获得对天气变率和污染物输送耦合的动力学机制的基本了解，(2)探索天气变率随温室气体浓度增加而变化如何改变这种输送。这两个目标将使用一系列模型来实现：一个大型多模型数据集、一个化学气候模型、一个平流层分辨率大气GCM和一个理想化的干燥动力核心。未来的污染物排放在很大程度上是不可预测的，但驱动对流层输送的动力过程有可能被理解。通过将排放与环流分离，这项工作旨在评估大气可变性的变化在改变对流层输送方面的作用。

Air quality over the western United States is determined not only by local emissions, but also by the transport of pollutants from outside the region, namely, from Asian emissions that have been transported across the Pacific Ocean, and by stratospheric intrusion events that bring naturally-occurring ozone-rich air to the surface. Quantifying the contribution of the large-scale atmospheric transport to present-day air quality is of vital importance for policy makers, since the ability of an area to be in compliance with current air quality standards is partly a function of the background meteorological conditions. Furthermore, increasing greenhouse gas concentrations over the next century are expected to drive large changes in the midlatitude circulation, but the effects of these changes on pollutant transport are not well understood.The goals of this project are (1) to gain a fundamental understanding of the dynamical mechanisms that couple synoptic variability and pollutant transport and (2) to explore how changes in synoptic variability with increased greenhouse gas concentrations may modify this transport. The two goals will be addressed using a hierarchy of models: a large-multi-model data set, a chemistry-climate model, a stratosphere-resolving atmospheric GCM and an idealized, dry dynamical core. Future pollutant emissions are largely unpredictable, but the dynamical processes that drive tropospheric transport have the potential to be understood. By decoupling emissions from the circulation, this work aims to assess the role of changing atmospheric variability in modifying tropospheric transport.