Understanding the Response of the Austral Jet Stream to Changes in Greenhouse Gases and Stratospheric Ozone

本研究的第一个目标是评估和归因在耦合模式比较项目第5阶段（CMIP5）综合气候模式中南半球急流对人为强迫的响应。首席研究员（PI）提出了一种简单的方法来划分臭氧和温室气体引起的变化对急流的影响。它将有助于更好地量化气候预测中的不确定性，将对温室气体和臭氧的热响应差异与喷射气流对大气温度变化的敏感性差异区分开来。将对CMIP5模式与上一代气候模式进行对比分析，以评估模式改进对气候预估的影响。CMIP3和CCMVal2是耦合模式比较项目第三阶段和化学气候模式验证活动2。本研究的第二个目标是通过一系列具有理想环流模型的控制实验，了解引起急流变化的机制。CMIP3和CCMVal2模式的初步分析表明，急流对对流层上层和平流层下层的温度梯度非常敏感，因此热带变暖或高纬度变冷时的响应是相似的。这暗示了温室气体和臭氧引起的变化背后的共同机制。此外，平流层臭氧引起的变化具有很强的季节足迹。PI将探索平流层和对流层背景季节循环与季节性局部臭氧强迫之间的相互作用。由于温室气体和臭氧的共同作用，在南半球夏季观测到的中纬度大气环流趋势比其他季节（或北半球）更强。这对整个南半球甚至热带地区的降水都产生了重大影响。因此，这个项目将增加我们对模型配置变化（例如，平流层的表示）如何影响模型响应的理解。这项研究将涉及一名研究生和一名博士后科学家，为他们作为研究科学家的发展提供机会。

The first goal of this research is to assess and attribute the response of the Southern Hemisphere jet stream to anthropogenic forcing in comprehensive climate models in the Coupled Model Intercomparison Project Phase 5 (CMIP5). The Principal Investigator (PI) suggests a simple method to partition the impact of ozone and greenhouse gas induced changes on the jet stream will be sugg. It will allow to better quantify uncertainty in climate projections, separating differences in the thermal response to greenhouse gases and ozone from differences in the sensitivity of the jet stream to changes in atmospheric temperature. Analysis of CMIP5 models to previous generation climate models from the Coupled Model Intercomparison Project Phase 3 (CMIP3) and Chemistry Climate Model Validation Activity 2 (CCMVal2) will be undertaken to assess the impact of model improvements on climate projection.The second goal of this research is to understand the mechanism(s) causing changes in the jet stream, using a series of controlled experiments with an idealized general circulation model. Preliminary analysis of CMIP3 and CCMVal2 models suggests that the jet is sensitive to the temperature gradient in the upper troposphere and lower stratosphere, so that the response is similar when the tropics are warmed or the high latitudes are cooled. This hints at a common mechanism behind greenhouse gas and ozone induced changes. In addition, stratospheric ozone induced changes have a strong seasonal footprint. The PI will explore interactions between the background seasonal cycle in the stratosphere and troposphere with a seasonally localized ozone-like forcing. Observed trends in the midlatitude circulation of the atmosphere are stronger in the Southern Hemisphere summer than in other seasons (or in the Northern Hemisphere), due to the combined effect of greenhouse gases and ozone. This has had significant impacts on precipitation throughout the Southern Hemisphere, even the tropics. Thus this project will increase our understanding of how changes in model configuration, e.g. representation of the stratosphere, impact a model's response. This research will involve a graduate student and postdoctoral scientist, providing opportunity for their development as a research scientists.