Transport and composition of the southern hemisphere UTLS (SOUTHTRAC)

对流层上层和平流层下层(UTLS)中水蒸气和臭氧等痕量气体分布的变化强烈地影响着辐射强迫以及地球的气候和表面温度，对于理解气候变化至关重要。由于大气辐射强迫对冷对流层顶区温室气体变化的高度敏感性，即使是平流层下部水汽的微小变化也是地表温度年代际变化的重要来源。UTLS中臭氧和水汽的未来变化也存在很大的不确定性，限制了预测21世纪平流层臭氧恢复和相关过程造成的辐射强迫的能力：几项研究表明，不同的化学气候模式甚至不能就臭氧恢复造成的辐射强迫的迹象达成一致，因为所模拟的组成存在很大的不确定性，特别是对流层顶附近的臭氧和水蒸气的变化。由于波的聚焦不同以及两个半球极涡的强烈差异，预计南半球和北半球UTLS的输送和组成会有很大的差异。尽管全球UTLS很重要，但尚未进行专门的实地部署，研究南部UTLS的运输过程和结构。以前的实地活动侧重于南极臭氧消耗和涡旋过程或热带或对流层的组成。此外，冬季南半球影响全球平流层环流，因为安第斯山脉构成了全球重力波活动的热点。这些波的传播和它们的影响还没有完全被理解。因此，我们提出了一个HALO运动，它涉及以下关于影响UTLS区域组成的过程的开放的关键方面：(1)南半球对流层顶的交换过程(2)南半球的重力波(3)生物质燃烧对南半球UTLS的影响(4)南极涡旋对UTLS的影响

Changes in the distribution of trace gases, like water vapor and ozone in the upper troposphere and lower stratosphere (UTLS) strongly impact radiative forcing and the Earth's climate and surface temperatures, and are of key importance for understanding climate change. Due to the high sensitivity of atmospheric radiative forcing to changes in greenhouse gases in the cold tropopause region even small variations e. g. in water vapour in the lower stratosphere are an important source of the decadal variability of the surface temperature. There is also large uncertainty in future changes of ozone and water vapour in the UTLS, limiting the ability to predict the radiative forcing due to stratospheric ozone recovery and related processes during the 21st century: Several studies  have shown that different chemistry climate models do not even agree on the sign of radiative forcing due to ozone recovery because of large uncertainties in modelled composition particularly ozone and water vapour changes in the vicinity of the tropopause. Due to different wave focing and strong differences in the polar vortices of both hemispheres, significant differences between transport and composition of the UTLS between the Southern and Northern Hemisphere are expected. Despite the importance of the global UTLS dedicated field deployments studying transport processes and structure of the southern UTLS have not yet been performed. Previous field campaigns focused on Antarctic ozone depletion and vortex processes or the tropics or tropospheric composition. In addition, the winter southern hemisphere affects the global stratospheric circulation since the Andes constitute a global hot spot for gravity wave activity. The propagation of these waves and their impact are not yet fully understood. Therefore, we propose a HALO campaign, which addresses the following open key aspects regarding the processes affecting the composition of the southern UTLS region: (1) Exchange processes at the southern hemisphere tropopause (2) Gravity waves in the southern hemisphere (3) Influence of biomass burning on the southern hemisphere UTLS (4) Impact of the Antarctic vortex on the UTLS