Sabine Brinkop

Aspects of convective activity and extreme events in a transient climate change simulation

Some aspects of the characteristic changes of convective activity in a warmer climate (following IPCC scenario IS92a), as simulated with the ECHAM4/OPYC GCM are analysed. Data of total rain, convective rain, convective height, frequency of convective events and mass fluxes are investigated for, both, the boreal summer (JJA) and the boreal winter (DJF) season. In either case the mean global convective rain rate and the frequency of deep convective events decrease from the 1981-90 decade to the 2071-80 decade (representative of 1×CO 2 and 2×CO 2 forcing), but the frequency of strong convective rain events, shallow convective events and the total rain rate increase. Thus, although the surface temperature is increased in the 2071-80 decade and more latent heat is available, deep convective events are reduced most pronounced on the southern hemisphere. These changes in convective activity are related to a change in the tropical circulation accounting for the effect of an interhemispheric asymmetry in surface warming in the 2×CO 2 climate similar to that reported by MURPHY and MITCHELL (1995).

On the theory of mass conserving transformations for Lagrangian methods in 3D atmosphere-chemistry models

Lagrangian methods were used in the past for dispersion modelling, air quality studies and climate-chemistry simulations, because they have a good representation of tracer transport. Here we show that air density inconsistencies between the Lagrangian representation and the model’s core grid can lead to substantial discrepancies. They affect any process calculation related to tracers on the model’s grid, both box and column processes, such as chemistry, photolysis, radiation, and sedimentation. This discrepancies can be resolved by using consistently Lagrangian methods for the core and (implicitely) for the tracer transport. Here we regard two Lagrangian methods, which divide the atmosphere by mass and present a transformation for these methods to derive a partitioning of the atmosphere in disjunct volumes and masses, which is a necessary pre-requisite to calculate any box or column process.

Global chemistry-climate modelling with EMAC

The Institute of Atmospheric Physics of the German Aerospace Center (DLR) uses the numerical model system ECHAM/MESSy Atmospheric Chemistry (EMAC). The model has a flexible modular structure and allows for coupled chemistry-climate simulations. Typical fields of application are related to questions regarding Earth’s climate, atmospheric chemical composition, and aerosol characteristics. In its current setup, the performance of EMAC on LRZ/ALTIX allows for multi-decadal simulations with climatologically significant results. The good performance demonstrates the multi-purpose capabilities of LRZ/ALTIX because EMAC involves various different numerical concepts and implementations of parallel decomposition. Our EMAC activities on LRZ/ALTIX are devoted to both model development and production simulations. The former comprise a new upper-boundary representation, a chemistry-transport mode, the inclusion of a mixed-layer ocean, and full-Lagrangian transport and dynamics. The latter tackle, for instance, questions related to the environmental impact of anthropogenic aerosol and gaseous substances.