Trace Gas Budgets and Interhemispheric Differences of Composition and Transport in the UTLS

UTLS区域（对流层上层/平流层下层，即8-20 km之间的区域）的组成对气候和地表温度起着基本的作用。该地区的微量气体收支是由小尺度湍流、斜压破裂波和行星波以及平流层环流等动力学过程决定的。由此产生的组成变率导致气候模拟和对未来地表气候的估计存在很大的不确定性。因此，以测量为基础的气团起源、输送过程和时间尺度的量化对于定量了解该地区至关重要。最近的测量主要集中在北半球，并显示了北半球UTLS成分的明显季节性循环。在夏季，特别是来自热带和季风区的短时间尺度的运输占主导地位，而在冬季，长时间尺度和老化的平流层气团的绝热下降占主导地位。对流层的贡献根据季节变化在20-60%之间。与运输有关的主要大气结构（例如极地涡旋和亚洲夏季风）引入了强烈的半球不对称，因此季节不对称组成、年龄和运输结构。基于测量的气团预算和南半球UTLS的量化仍然缺失。在这个项目中，这个预算将根据示踪剂测量和与北半球的比较进行量化，包括空气质量分数和运输时间尺度。这将包括研究有助于南半球内部以及两个半球之间的运输和混合的有关过程。

The composition of the UTLS region (upper troposphere / lower stratosphere, i.e. the region between 8-20 km) plays a fundamental role for climate and surface temperatures. The trace gas budget of this region is determined by dynamical processes, which range from small scale turbulence, over breaking baroclinic and planetary waves to the stratospheric circulation. The resulting variability of the composition leads to significant uncertainties of climate simulations and estimates of future surface climate. A measurement based quantification of air mass origin, transport processes and time scales is therefore essential for a quantitative understanding of this region.Recent measurements mainly focused on the northern hemisphere and showed a clear seasonal cycle of the composition of the northern UTLS. During summer short transport time scales of weeks for transport particularly from the tropics and the monsoon region dominate the northern UTLS, whereas in winter long time scales and diabatic descent of aged stratospheric air masses prevail. The tropospheric contribution varies between 20-60% depending on season.The dominating atmospheric structures relevant for transport (e.g. the polar vortex and the Asian summer monsoon) introduce a strong hemispheric asymmetry and therefore seasonal asymmetric composition, age and transport structures. A measurement based air mass budget and quantification of the southern hemisphere UTLS is still missing. Within this project, this budget will be quantified on the basis of tracer measurements and the compared with the northern hemisphere including air mass fractions as well as transport time scales. This will include a study of the relevant processes which contribute to transport and mixing within the southern hemisphere, but also between both hemispheres.