Lokal Modell

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Overview of the
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1. Contact

Dr. Kai Born
Meteorological Institute
University of Bonn
Auf dem Hügel 20
D-53121 Bonn

Tel.: +49 (0) 228 73 5194
Fax: +49 (0) 228 73 5188
email: kborn@uni-bonn.de

2. Short Description

New parameterisations for radiative transfer will be implemented in the non-hydrostatic Lokal Model in the modelling component of the 4D-CLOUDS project. With this enhanced model the influence of the three dimensional clouds on the exchange processes of sensible and latent heat in the boundary layer will be investigated.

3. Model characteristics and features

The Lokal-Modell of the DWD is a non-hydrostatic limited area atmospheric prediction model. It is designed for operational numerical weather prediction as well as various scientific applications on the mesoscale (50 - 0.5 km). The model is based on the primitive thermo-hydrodynamical equations describing compressible flow in a moist atmosphere. A variety of physical processes are taken into account by parameterisation schemes. LM 2.1 runs on conventional scalar machines (e.g. IBM and SGI workstations), vector supercomputers (e.g. CRAY-YMP, CRAY-C90 and Fujitsu VPP700) and MPP machines with an implementation of the MPI library for message passing. Below the features of version 2.1 are listed.

Non-hydrostatic, full compressible, no scale approximations.

Co-ordinate System
Generalised terrain-following vertical co-ordinate and rotated geographical co-ordinates. Equidistant grid spacing in the horizontal directions and user defined grid stretching in the vertical.

Model Geometry
1-D, 2-D and 3-D model configurations. Metrical terms can be adjusted to represent tangential Cartesian geometry with constant or zero Coriolis parameter.

Prognostic Variables
Physical components of wind velocity respective the orthogonal z-system, perturbation pressure, temperature, specific humidity, cloud water content and (optionally) cloud ice content.

Diagnostic Variables
Total density, precipitation, fluxes of rain and snow.

Spatial Discretisation
Second-order, finite differences for advection and other terms on an Arakawa C-grid. Vertically, the Lorenz-grid is used for the staggering of model variables.

Time Discretisation
Second-order leapfrog for large time steps with Asselin time filter. First order forward-backward scheme for small time steps.

Time Integration
Split-explicit with vertically implicit option for sound and gravity wave propagation.

Initial Conditions
Options for real data cases with interpolated initial data from a coarse-grid driving model and user-specified idealised initial fields.

Initialisation of unbalanced initial states using a digital, filter. Options for adiabatic and diabatic initialisation.

Subgrid Scale Turbulence
Diagnostic second order closure of hierarchy level 2 for vertical turbulent, fluxes. Options for turbulent kinetic energy formulation and isotropic as well as an-isotropic 3-D treatments of turbulence to be added.

Surface Layer Parameterisation
Stability-dependent drag-law formulation of momentum, heat and moisture, fluxes according to similarity theory.

Grid Scale Clouds and Precipitation
Options for a warm-rain (Kessler scheme), a 1-category ice (from EM/DM) and a 2-category ice (cloud ice scheme) bulk parameterisation of cloud microphysics. Further options to be added.

Longwave and Shortwave Radiation
The radiation scheme employs eight spectral intervals and is based on the solution of the two-stream version of the radiative transfer equation. Direct radiation interaction with cloud water and cloud ice is allowed for. Subgridscale cloudiness is diagnosed from relative humidity.

Soil Model
Two-layer model for heat budget formulated according to the extended force-restore method. Two-layer or optionally three-layer model for the water budget including interception storage of water and snow.

Cumulus Parameterisation
Tiedtke mass-, flux scheme for non-resolvable moist convective processes with equilibrium closure. Scheme with non-equilibrium closure to be added.

Terrain and Surface Data
Orography, soil and land-use data are available at 0.0125, 0.025, and 0.06 degrees model resolution for the domain of DM (covering Germany and surrounding countries).