Modelling the changes in the upper tropospheric composition due to convective transport

Abstract

Atmospheric moist convection has a considerable influence on the composition of the upper troposphere. Besides the strong effects on the atmospheric moisture budget, the high vertical velocities associated with deep convection lead to a redistribution of air masses, with especially large effects on the concentration of tracers with short atmospheric lifetimes. Even though the importance of convective transport is long known, this process remains a major source of uncertainty. To diagnose the efficacy of convective tracer transport, we have developed a new modelling tool for simulations in global circulation models that rely on convection parameterisations, namely the convective exchange matrix. The exchange matrix basically links fractional contributions of inflow and outflow between any model level when convection is simulated for a given column. We apply this new tool in the chemistry climate model EMAC (ECHAM5 MESSy Atmospheric Chemistry) in order to characterise the transport of individual convective events. Beyond that, we present long-term statistics on vertical tracer transport into the upper troposphere to highlight the contribution of air masses originated at different heights to the upper tropospheric composition. This also includes the analysis of the regional and global distribution of convective outflow heights of the simulated convective clouds. Finally, we outline a potential application as a support tool for the analysis of upper troposphere aircraft observations in convectively active regions to backtrace the origin of the air masses and their overall contribution to the measured concentrations.