General Description: Model Physical Parameterizations

see also: dynamics and numerics | initial and boundary conditions | basic design | external parameters | code and parallelization | data assimilation
Last updated: September 2011

A variety of subgrid-scale physical processes are taken into account by parameterization schemes. Some parts of the present physics package of the COSMO-Model have been adapted from the former operational hydrostatic models EM/DM, but some are based on new developments or have been taken over by GME or the IFS. The following table gives a short overview on the parameterization schemes used operationally and on additional options implemented so far.

Grid-Scale Clouds and Precipitation
  • Cloud water condensation and evaporation by saturation adjustment.
  • Precipitation formation by a bulk microphysics parameterization including water vapour, cloud water, cloud ice, rain and snow with 3D transport for the precipitating phases.
  • Option for a new bulk scheme including graupel.
  • Option for a simpler column equilibrium scheme.
Subgrid-Scale Clouds
  • Subgrid-scale cloudiness is interpreted by an empirical function depending on relative humidity and height. A corresponding cloud water content is also interpreted. Option for a statistical subgrid-scale cloud diagnostic for turbulence.
Moist Convection
  • Tiedtke (1989) mass-flux convection scheme with equilibrium closure based on moisture convergence. Option for a modified closure based on CAPE.
  • Reduced Tiedtke scheme for shallow convection only.
  • δ-two stream radiation scheme after Ritter and Geylen (1992) for short- and longwave fluxes (employing eight spectral intervals); full cloud-radiation feedback.
Subgrid-Scale Orography
  • Subgrid-scale orography (SSO) scheme by Lott and Miller (1997) which deals explicitly with a low-level flow that is blocked when the subgrid-scale orography is sufficiently high.
Subgrid-Scale Turbulence
  • Prognostic turbulent kinetic energy closure at level 2.5 including effects from subgrid-scale condensation and from thermal circulations.
  • Option for a diagnostic second order K-closure of hierarchy level 2 for vertical turbulent fluxes.
  • Preliminary option for calculation of horizontal turbulent diffusion in terrain following coordinates (3D Turbulence).
Surface Layer
  • A Surface layer scheme (based on turbulent kinetic energy) including a laminar-turbulent roughness layer.
  • Option for a stability-dependent drag-law formulation of momentum, heat and moisture fluxes according to similarity theory (Louis, 1979).
Soil Processes
  • Multi-layer version of the former two-layer soil model after Jacobsen and Heise (1982) based on the direct numerical solution of the heat conduction equation. Snow and interception storage are included.
  • Option for the (old) two-layer soil model employing the extended force-restore method still included.
Sea Ice Scheme
  • Based on work by Mironov and Ritter (DWD)
FLake Model
  • A Fresh-water Lake model by Mironov (2008)