Project B01:
Fine scale composition gradients and mixing at the tropopause region

Brief Summary

In this project we will use a combination of in-situ measurements with modelling on different scales (employing several nested domains) to investigate the effect of small scale diabatic processes associated with cirrus occurrence and turbulence on the vertical gradients of humidity, trace gases and aerosols at the tropopause. We will combine a novel aircraft based approach using two measurement platforms with a state-of-the-art high resolution model system MECO(n), which allows convection permitting simulations from the sub-km-scale to the synoptic and global scale including comprehensive aerosol and chemical simulations.
The aircraft measurements will be partly performed with a dual platform system, measuring humidity, (potential) temperature, ozone, aerosol size distribution and backscatter simultaneously at two different altitudes separated typically less than 300 m. Therefore, we can deduce isentropic gradient changes of the UTLS composition particularly for highly transient small scale processes associated with cirrus clouds variability or turbulent mixing at the tropopause. With this setup we will identify cirrus internal convection and its potential effect on the chemical and thermodynamical structure of the tropopause region – specifically water and ozone, but also aerosols at the tropopause.
To put the local scale observations into a larger scale we will use simulations with the MECO(n) system, which includes the possibility to simulate processes utilizing nesting options with several nests for a dynamical downscaling with a grid size of a few 100 m and sample data along the flight track. Combined with its comprehensive chemistry and aerosol schemes this provides the unique possibility to study the processing of the chemical composition of air masses across scales and analyzing the impact of the composition on dynamics of the tropopause region.
This includes transport and processing of boundary layer aerosol and precursors to the extratropical tropopause by mid latitude convection and frontal uplift. We will focus on the evolution and representation of gradients of these species downwind these systems in different model resolutions. To infer information on mixing at the tropopause we will develop a novel representation of mixing particularly focusing on clear air turbulence (CAT) under different synoptic situations associated with mid-latitude cyclones especially in the ridges and above the jets of these systems. With the model the analysis will be put in a larger context, to estimate the importance of the underlying small scale processes on the regional and synoptic scale.

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