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Most of our work is conducted with the Bremen 3D Chemistry and Transport Model (B3DCTM). It is an offline chemistry and transport model driven by external meteorological input, for example from the European Centre for Medium-Range Weather Forecasts (ECMWF). The spatial resolution is variable but for performance reasons most runs are conducted with a resolution of 2.5° in latitudinal and 3.75° in longitudinal direction. The vertical coordinate is potential temperature, i.e. the model space is layered in isentropes ranging typically from 330 to 2700 K (about 10 to 55 km) with 24 levels.

The horizontal transport on isentropes is calculated from the meteorological wind field data whereas the vertical velocity is derived from heating rates, either calculated online by a radiation scheme or offline based on archived input. Additionally, we have incorporated a parametrization of convective transport based on archived detrainment rates which can be used optionally.

The model structure is fully modularized to serve the needs of different kinds of tasks. Depending on the current requirement different independent modules can be inserted in the model workflow, such as a detailed or idealized chemistry scheme, an assimilation routine for observational data or the inclusion of specific processes like precipitation of high-energetic solar particles. The model is fully parallelized with OpenMP to take advantage of multiprocessor-architectures.

Fig. 1: Horizontal resolution of the CTM.  Fig. 2: Potential temperature levels of the CTM.