Air mass export from the Asian monsoon into theextratropical stratosphere: impact on chemistry and radiation (AirExam)

亚洲夏季风与亚洲季风反气旋（AMA）有关，从对流层上部延伸到平流层下部（UTLS）区域，这是北方夏季这些高度最明显的环流模式。据了解，准等熵输出的季风空气的AMA的东部和西部有很大的影响外对流层低平流层的组成，但它们的相对强度是未知的。从AMA到北外热带UTLS的空气质量输送对平流层化学及其辐射收支（例如，通过H2O、气溶胶或臭氧消耗物质的迁移）。在这个项目中，AirExam将通过不同的途径从AMA输出准等热带气团到ExUTLS，并将使用i.a. HALO飞机测量（特别是计划于2023年夏季进行的PHILEAS活动）、化学传输模式CLaMS模拟和辐射计算。我们的项目AirExam将解决以下关键的开放性问题：1）亚洲季风反气旋的两条准水平传输路径（向西和向东）对对流层外平流层下部组成的相对贡献是什么？2)从亚洲季风反气旋向对流层外平流层低层输送的年内变率有多大，地球表面的主要源区是什么？3)亚洲季风反气旋水汽输送对热带外UTLS的H2O收支及其辐射影响有什么影响？在我们的项目中，我们将结合联合收割机HALO测量（特别是H2O）与全球三维CLaMS模拟，包括人工示踪剂的空气质量的起源，以及'路径查找器示踪剂'。 CLaMS模拟将由新的ECMWF ERA-5再分析驱动，提供比旧的ERA-Interim产品更高的空间和时间分辨率。由ERA-5驱动的CLaMS模拟是一种独特的工具，可以可靠地描述亚洲季风地区的输送过程及其全球影响。利用Edwards和Slingo辐射传输程序计算了夏季和秋季亚洲季风引起的H2O增加的辐射影响。 H2O是最重要的温室气体，平流层的增湿是气候变化的重要驱动力。我们的项目AirExam将量化增强的H2O输送到平流层下部的影响，因此可以帮助评估亚洲季风区的空气质量输送对全球平流层的潜在风险。

The Asian summer monsoon is associated with deep convection over south Asia linked to the Asian monsoon anticyclone (AMA) that extends from the upper troposphere into the lower stratosphere (UTLS) region, which is the most pronounced circulation pattern in these altitudes during boreal summer. It is known that the export of monsoon air quasi-isentropically out of the AMA both to the east and to the west has a large impact on the composition of the extratropical lower stratosphere, however their relative strengths is unknown hitherto. The transport of air masses out of the AMA into the northernextratropical UTLS crucially affects stratospheric chemistry and its radiative budget (e.g., through transport of H2O, aerosol or ozone-depleting substances). Within this project AirExam the quasi-isentropical air mass export from the AMA by different pathways into ExUTLS and its impact on chemistry and radiation will be quantified using i.a. HALO aircraft measurements (in particular from the PHILEAS campaign scheduled for summer 2023), simulations with the Chemical Transport Model CLaMS and radiative calculations.Our project AirExam will address the following key open questions:1) What are the relative contributions of the two quasi-horizontal transport pathways (to the west and to the east) out of the Asian monsoon anticyclone to the composition of the extratropical lower stratosphere?2) How large is the intra-annual variability of the transport out of the Asian monsoon anticyclone to the the extratropical lower stratosphere and what are the main source regions on the Earth’s surface?3) What is the impact of water vapor transport out of the Asian monsoon anticycloneto the H2O budget of the extratropical UTLS and its radiative impact?In our project, we will combine HALO measurements (in particular H2O) with global 3-dimensional CLaMS simulations including artificial tracers of air mass origin as well as 'pathway finder tracers'. CLaMS simulations will be driven by the new ECMWF ERA-5 reanalysis providing a much higher spatial and temporal resolution than the older ERA-Interim product. CLaMS simulations driven by ERA-5 are a unique tool to describe transport processes reliably in the region of the Asian monsoon and its global impact. The radiative impact of the H2O increase during summer and autumn caused by the Asian monsoon will be calculated using Edwards and Slingo radiative transfer code. H2O is the most important greenhouse gas and moistening of the stratosphere is an important driver of climate change. Our project AirExam will quantify the impact of enhanced H2O transport into the lower stratosphere and therefore can help to assess the potential risks of air mass transport from the Asian monsoon region on the global stratosphere.