Gravity Waves and Trace Gas Mixing in the Arctic Winter Tropopause Region

在这个项目中，我们将对对流层顶的输送和交换过程进行空中观测，对流层顶构成了大体上混合良好的对流层和稳定的层结平流层之间的边界。这一网状区对大气的辐射收支起着重要的作用，因此，由于混合而引起的化学成分的微小变化可能直接影响辐射活性物质，进而影响表面温度。北极冬季三层顶区域的空中测量将特别侧重于地形激发的重力波对痕量气体输送和混合的作用，并查明相关条件和潜在过程。因此，我们将使用CO和N2O的高精度测量作为运输的示踪剂。特别是，N2O是一种有价值的大气动力学示踪剂，因为它在对流层中几乎是惰性的，在对流层中几乎均匀分布。由于它的惰性和平流层垂直梯度，它允许测量整个平流层中由波引起的示踪剂扰动。对流层顶垂直梯度较弱，对其量化精度要求很高。自2013年8月以来，美因茨大学大气物理研究所拥有一台仪器，其仪器精度达到了N2O的仪器精度，这是解决这种梯度所必需的。利用这台仪器，我们将在瑞典北部基律纳的德国航天中心研究飞机“猎鹰”上进行测量，这是一个有利于产生重力波的条件：1)确定这种波对痕量气体分布的影响，并探测波诱导湍流的局部发生2)确定和量化跨对流层痕量气体交换的相关波长和时间尺度3)确定波诱导的跨对流层的示踪剂通量4)确定导致波诱导湍流和混合的相关过程。由于N2O测量的精度有限，这种基于航空现场数据和N2O和CO相关性的混合和湍流的量化到目前为止是不可能的。结合猎鹰飞机的风和湍流测量，可以量化波浪诱导的示踪通量，并确定这些通量的相关波长。与EULAG模型进行比较，可以确定导致波浪诱导湍流和微量气体混合的小尺度大气过程。

Within this project we will perform airborne observations of transport and exchange processes at the tropopause, which constitutes the boundary between the generally well-mixed troposphere and the stable stratified stratosphere. This perticular region plays an important role for the radiation budget of the atmosphere, such that small changes of the chemical composition due to mixing may directly affect radiatively active species, which in turn influence the surface temperatures. The airborne measurements in the arctic winter triopopause region will focus especially on the role of orographically ijndiuced gravity waves for trace gas transport and mixing and to identify the relevant conditions and underlying processes. Therefore we will use high precision measurements of CO and N2O as tracers of transport. Particularly N2O is a valuable tracer for atmospheric dynamics, since it is virtually inert in the troposphere and almost homogenously distributed in the troposphere. Due to its inertness and its stratospheric vertical gradient it allows to measure wave induced tracer perturbations throughout the stratosphere. The vertical gradient at the tropopause is only weak, which requires a very high precision for its quantification. Since August 2013 the institute for atmospheric physics of the university Mainz owns an instrument, with the instrumental precision for N2O, which is required to resolve this gradient. With this instrument we will perform measurements onboard the DLR research aircraft Falcon in Kiruna (Northern Sweden), which is a reguion favourable for the generation of gravity waves to:1) identify the effect of such waves on the trace gas distribution and to probe local occurrence of wave induced turbulence2) identify and quantify the relevant wavelengths and time scales for trace gas exchange across the tropopause3) determine wave induced tracer fluxes across the tropopause4) identify the relevant processes which lead to wave induced turbulence and mxing. Such a quantification of mixing and turbulence on the basis of airborne in-situ data and correlations of N2O and CO was so far not possible due to the limited precision of the N2O measurements. The combination with the wind and turbulence measurements of the FALCON aircraft allows quantifying wave induced tracer fluxes and to identify the relevant wave lengths for these fluxes.The comparison with the EULAG model allows to identify the relevant atmospheric processes on the small scale which lead to wave induced turbulence and trace gas mixing.