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运输和交换过程进行空中观测，对流层顶构成了混合良好的对流层和稳定的分层平流层之间的边界。这一特定区域对大气的辐射收支起着重要作用，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，进而影响地表温度。北极冬季三对流层顶区域的航空测量将特别侧重于地形诱导重力波对微量气体输送和混合的作用，并确定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，并且在对流层中几乎均匀分布。由于它的惰性和它的平流层垂直梯度，它允许测量整个平流层的波诱导示踪扰动。对流层顶的垂直梯度很弱，这就要求对其进行量化的精度很高。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，其仪器精度为N2O，需要解决这个梯度。有了这个仪器，我们将在基律纳（瑞典北部）的DLR研究飞机猎鹰上进行测量，这是一个有利于产生重力波的区域，以便：1)确定重力波对微量气体分布的影响，探测波致湍流的局部发生；2)确定和量化穿过对流层的微量气体交换的相关波长和时间尺度；3)确定穿过对流层的波致示踪剂通量；4)确定导致波致湍流和混合的相关过程。由于N2O测量的精度有限，这种基于机载原位数据和N2O和CO相关性的混合和湍流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，可以量化波诱导示踪剂通量，并确定这些通量的相关波长。通过与EULAG模式的比较，可以在小尺度上识别出导致波致湍流和微量气体混合的相关大气过程。

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.