FLEXPART for COSMO output

TOGether with MeteoSwiss our group developed a new version of the widely used Lagrangian Particle Dispersion Model (LPDM) FLEXPART for output from the regional numerical weather prediction (NWP) model COSMO. We mainly run FLEXPART-COSMO with operational analysis fields as generated hourly by MeteoSwiss for Western Europe with a horizontal resolution of approximately 7 km x 7 km and a nested grid over the Alpine area with 2 km x 2 km resolution. However, the application of FLEXPART-COSMO is not limited to MeteoSwiss output but can be used with any grib formatted COSMO output that includes a minimal set of variables.

The main differences between FLEXPART-COSMO and standard FLEXPART-ECMWF are the internal vertical grid representation and the parameterisation of convective transport. In FLEXPART-COSMO the native vertical grid of the COSMO model is used as the main frame of reference, whereas standard FLEXPART uses a terrain following height-based vertical coordinate with constant height shifts up to the model top. The latter requires an initial vertical interpolation from model input on pressure-based hybrid coordinates as used in the standard input from ECMWF. In FLEXPART-ECMWF sub-grid scale convection is treated by an Emanuel type scheme. A different parameterisation of convective transport was implemented into FLEXPART-COSMO. In order to stay as close as possible to the convective transport as simulated in COSMO itself, the same modified version of the Tiedtke convection scheme as in COSMO was implemented.

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Annual mean source-receptor relationship for Beromünster tall tower site.

In our group FLEXPART-COSMO is mainly used to calculate high resolution source-receptor relationships for atmospheric surface measurements in the larger Alpine domain (for example those of our high altitude site Jungfraujoch and those of the CarboCount-CH network). The high horizontal resolution used in FLEXPART-COSMO allows for a more realistic description of the complex flow patterns in Alpine terrain that cannot be achieved with standard FLEXPART, which is currently limited to horizontal resolutions of about 20 km x 20 km. Source-receptor relationships give the direct influence of a mass emission from a source location onto the mole fraction at a receptor site. Hence, they can be directly used in inversion emission modeling at the regional scale and the complex Swiss environment.




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