The Role of Water Vapor in Midlatitude Stormtracks and the Global Circulation

最近，首席研究人员和他的合作者对等熵环流的研究表明，中纬度地区的极地质量输送分为对流层上层的“干支流”和风暴带内低层暖湿副热带气流的“湿支流”。该项目将开发一个新的框架，以更好地评估局地和全球尺度上降水和中纬度天气系统之间的关系，并将评估不同气候条件对全球环流的影响。它试图更好地了解(1)是什么控制了这些干湿分支之间的环流分配，(2)这种分配如何影响环流的能量和动量输送，(3)对单个风暴的影响是什么，以及(4)这种影响在未来可能如何变化，无论是自然气候变化的结果，还是人为温室气体排放的结果。本文的方法是基于分析干等温面或湿等温面上平均的纬向平均环流。这项研究包括评估湿过程对中纬度天气系统动力学的作用的理论发展，斜压生命周期和全球大气的数值模拟，以及根据再分析数据集对当前环流的综合研究。还将开发一套诊断工具来评估数值模式中的等熵环流，并向更广泛的社区提供。拟议研究的更广泛影响是有可能提高我们预测气候变化如何影响副热带和中纬度天气的能力，并改变全球降雨量的分布。将仔细评估政府间气候变化专门委员会(IPCC)使用的不同全球气候模型，并将其与再分析数据进行比较。这既应该表明改进这些模型的可能方法，也应该增加我们对它们准确模拟气候系统和水文循环能力的信心。

A recent study of the isentropic circulations by the principal investigator and his collaborators has shown that the poleward mass transport in the mid-latitudes is equally split between a "dry branch" in the upper troposphere, and a "moist branch", associated with a low level poleward flow of warm, moist subtropical air that ascends in the upper troposphere within the stormtracks.This project will develop a new framework to better assess the relationship between precipitation and mid-latitude weather systems on both the local and global scales, and will evaluate how the global circulation is affected by different climatic conditions. It seeks a better understanding of (i) what controls the partitioning of the circulation between these dry and moist branches, (ii) how does this partitioning affect the energy and momentum transport by the circulation, (iii) what are the implications at the level of the individual storm, and (iv) how this might change in the future either as a result of natural climate variability or as a consequence of anthropogenic greenhouse gas emissions. The approach here is based on analyzing the zonal mean circulation averaged on either dry isentropes, i.e., surfaces of constant potential temperature, or moist isentropes, i.e., surfaces of constant equivalent potential temperature. The research includes theoretical development to assess the role of moist processes on the dynamics of mid-latitude weather systems, numerical simulations of baroclinic life-cycle and of the global atmosphere, and a comprehensive study of the current circulation based on reanalysis datasets. A set of diagnostic tools to assess the isentropic circulation in numerical models will also be developed and made available to the broader community.Broader impacts of the proposed research are in the potential to improve our ability to predict how climate change can affect subtropical and mid-latitude weather, and modify the global distribution of rainfall. Different global climate models used by the Intergovernmental Panel on Climate Change (IPCC) will be carefully evaluated and compared to reanalysis data. This should both indicate possible ways to improve these models, as well as increase our confidence in their ability to accurately simulate the climate system and the hydrological cycle.