Understanding seasonality and trends of transport pathways and composition in the upper troposphere lower stratosphere (UTLS) region

输送路径的季节性和趋势影响对流层上部、下部平流层(UTLS)的痕量气体组成，而UTLS又影响辐射强迫和气候变化。目前，UTLS的运输及其与气候变化的联系是大气科学中一个迅速扩大的领域。这项在美国博尔德的国家大气研究中心(NCAR/ACD)设立研究奖学金的提议旨在开发新的诊断工具，以更好地了解UTLS的运输路径，特别关注季节性和趋势及其对痕量气体成分的影响。利用化学输送模式CLAMS和气候模式WACCM--一种计算平流层空气年龄谱的新诊断工具，将根据各种衰变示踪物，开发起源于热带对流层顶的气团输送时间尺度的概率分布。考虑年龄谱是超越目前主要考虑平均年龄的研究的重要一步。该方法将根据脉冲实验的年龄谱和弹道穿越时间分布进行验证。新的年龄谱诊断将应用于CLAMS和WACCM模型，作为模型迁移评估的工具。不同年龄谱诊断和轨迹统计的结合将为热带和温带低平流层之间不同路径的相对强度和季节性以及长期环流趋势提供新的深入见解。因此，拟议的工作将是朝着更好地了解我们不断变化的气候系统迈出的重要一步。

Seasonality and trends in transport pathways affect the trace gas composition of the upper troposphere lower stratosphere (UTLS) which, in turn, impacts radiative forcing and climate change. Currently, transport in the UTLS and its link to a changing climate is a rapidly expanding field in atmospheric science. This proposal for a research fellowship at the National Center for Atmospheric Research (NCAR/ACD) at Boulder/USA aims at developing novel diagnostic tools for an improved understanding of transport pathways in the UTLS, with particular focus on seasonality and trends and the impact on trace gas composition. Using the chemistry transport model CLaMS and the climate model WACCM, a new diagnostic tool for calculating the age spectrum of stratospheric air, the probability distribution of transport time scales of air parcels originating at the tropical tropopause, will be developed, based on various decaying tracers. Considering the age spectrum is a major step forward going beyond current research where mainly the mean age is considered. The method will be validated against age spectra from pulse experiments and against trajectory transit time distributions. The new age spectrum diagnostic will be applied to the CLaMS and WACCM models as a tool for model transport evaluation. The combination of the different age spectrum diagnostics and trajectory statistics will provide new deep insight into the relative strength and the seasonality of different pathways between the tropical and the extratropical lower stratosphere and long-term circulation trends. Hence, the proposed work will be an important step towards an improved understanding of our changing climate system.