Mesoscale models

Mesoscale models are numerical tools which resolve atmospheric processes of spatial scales between 2 and 1000 km. They solve the conservation equations of mass, momentum, internal energy and diverse air constituents (for example water vapour, trace gases or aerosol) with different physical approximations (incompressible, anelastic; hydrostatic, non-hydrostatic). Small-scale physical processes that are not resolved by the chosen temporal and spatial discretization (mesh width, time step), such as boundary-layer turbulence or convective exchange processes, are parameterized by ad-hoc approaches, i.e. they are approximately described by resolved parameters.

Mesoscale models are mostly specialized for distinct applications (e.g. regional or local weather forecast or process studies). Therefore, different mesoscale models are applied at the Institute for Atmospheric Physics to different problems. Three examples are

  • the model COSMO (Consortium for small-scale modeling) of the German Weather Service which is operated as COSMO/MESSy (Modular Earth submodel system) by single or multiple nesting, especially to regionally refine the coarse-grid the global model EMAC.
  • the model EULAG (Eulerian/semi-Lagrangian numerical model for fluids) with several modules (developed in cooperation with our institute) to treat the microphysics of ice clouds and of condensation trails.
  • the HYSPLIT (hybrid single-particle Lagrangian integrated trajectory) model for the calculation of forward- and backward trajectories, as well as for plume dispersion. HYSPLIT is driven kinematically, e.g. by meteorological fields of the Global Data Assimilation System (GDAS) or ECMWF. We operate HYSPLIT within a user-friendly, IPA-developed framework. This model system is one of our workhorses for flight-planning during aircraft measurement campaigns and subsequent data analyses.  
  • the Weather Research and Forecasting (WRF) model, which is a flexible atmospheric modelling system serving a wide range of meteorological applications across scales from tens of meters to thousands of kilometers. It’s a widely used community model, supported by the National Center for Atmospheric Research (NCAR). IPA uses WRF for the simulation of gravity waves and turbulence, for processes in the atmospheric boundary layer related to wind energy research, as well as for interpretation and evaluation of in situ and remote sensing measurements on greenhouse gases and other atmospheric trace species.

Further important applications of mesoscale models are, for example, local heavy precipitations events, convective storms, and regional climate studies.