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层和平流层下层（UTLS）的微量气体组成，进而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发展的领域。美国博尔德国家大气研究中心（NCAR/ACD）的研究奖学金提案旨在开发新的诊断工具，以更好地了解UTLS的运输途径，特别关注季节性和趋势以及对微量气体组成的影响。利用化学输运模式CLaMS和气候模式WACCM这一计算平流层空气年龄谱的新诊断工具，基于各种衰变示踪剂，建立了源自热带对流层顶的空气包裹输运时间尺度的概率分布。考虑年龄谱是一个重大的进步，超越了目前主要考虑平均年龄的研究。该方法将根据脉冲实验的年龄谱和轨道传输时间分布进行验证。新的年龄谱诊断方法将作为模型迁移评价工具应用于CLaMS和WACCM模型。不同年龄谱诊断和轨迹统计相结合，将对热带和温带平流层下层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认识。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.