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

• Applicant: Professor Dr. Peter Hoor
• Subject Area: Atmospheric Science
• Term: from 2016 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 282657310

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.

• DFG Programme: Research Grants