METRAS

The METRAS model has originally been developed at Meteorological Institute, University of Hamburg (Schlünzen, 1988, 1990). In the meantime it is broadly used in Germany and overseas. METRAS can be used for areas between 10 km x10 km (e.g. convection) and 2500 km x 2500 km (e.g. coastal convergences, pollution transport in a regional scale, cyclone development). A 3d non-uniform grid allows higher resolution in interesting areas and close to the surface with a reduced resolution in other regions. Wind, temperature, humidity, cloud- and rainwater as well as tracer concentrations are calculated from prognostic equations, pressure from the (diagnostic) anelastic equation. The influence of several land use characteristics (e.g. water, urban areas, vegetation, ice) as well as of orography (mountains, cliffs, houses) is considered in the model using flux averaging with blending height concept. The dry deposition of pollutions is calculated from a resistance model, it depends on pollution and land use characteristics. Chemical transformations are included in the off-line coupled chemistry transport model MECTM.

The lateral model boundaries are open or METRAS is nested in results of a coarser model (e.g. weather forecast, analysis or regional climate model). At the model top absorbing layers are used, or again the nesting technique is applied. By use of the model system M-SYS which employs METRAS and MECTM in several resolutions concentrations of several pollutants (e.g. NO_x, O₃, SO₂ , NH₃, Pb, nitrate, sulphate) in the air and the deposition at the ground can be calculated dependent on the sources (industry, power stations, household, car and ship traffic). Emission scenario studies can be performed.