Project C07:
The composition of the global UTLS nowadays and at the end of the 21st century

Brief Summary

In this project we will conduct and analyze computer simulations with the chemistry climate model EMAC, which participates in the AerChemMIP multi-model intercomparison project (as part of CMIP6) to investigate the evolution of the chemical composition of the UTLS on the global scale. The analysis will focus on the one hand side on the inter-hemispheric differences of the chemical composition of the UTLS and the temporal behaviour of both trace gas and aerosol concentrations as deduced from hindcast experiments in comparison with observations, and also an analysis for up to future chemistry-climate projections (following scenarios developed within the framework of CMIP6). The radiatively active compounds also play a substantial role for the climate sensitivity of chemistry climate models, which is mainly driven by the radiative forcing of the individual radiative active compounds, but also the inherent feedback processes.
In this project phase we will focus on the sensitivity of the radiative forcing by process parameterizations, from which in a later stage a climate sensitivity of the model can be deduced. The current project plan will also focus on a quantification of the chemistry-climate interactions of ozone, water vapour and aerosol particles (both direct aerosol-radiation interactions and aerosol-cloud-radiation interactions) and associated feedback processes in the UTLS with implications for the whole atmosphere from the surface to the stratopause. In addition to the analysis of existing model simulations, we will conduct specific sensitivity simulations to estimate the effect of parameterized processes (in this project convection) on the UTLS chemical composition with the help of sensitivity simulations to quantify 1) the impact of the respective processes on the composition and 2) a sensitivity of the climate response via its associated radiative forcings to the representation of these processes.
Therefore, it is the goal of the project to also analyse the impact of chemistry-aerosol-radiation interactions on the circulation patterns within the UTLS and resulting exchange fluxes between the troposphere and the stratosphere. A detailed analysis of the chemical composition of the UTLS, especially including aerosol particles and their chemical composition in the UTLS has hardly been undertaken so far; we also plan to include tagging to determine the origin of aerosol particles or the location of new particle formation events to estimate the role of transported versus in-situ formed aerosol particles for the aerosol budget of the UTLS and the role of chemistry-climate interactions. To evaluate the model simulations and the respective process representations we will make use of comprehensive observation data sets, e.g. from the HALO database from recent campaigns, in which substantial data in the UTLS haves been acquired, and also the (e.g. the HALO database, IAGOS/CARIBIC/ and MOZAIC and additional campaign data. This will be conducted for both, the “specified dynamics” simulation, for which a point-to-point comparison can be made, as well as repeated for the other anticipated simulations in this project, for which a more statistically based analysis will be performed. Furthermore, this project provides opportunities for several other projects within the CRC to put individual and local results into the context of global chemistry-climate simulation data.

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