External Data
See also the documentation in RedC: EXTPAR
The information about climatologically constant data from the external data set are one source of information needed to create
forcing data for COSMO-CLM. EXTPAR is the main program for preparing the external data set. The interactive web frontend WebPEP (Web interface for Preprocessing External data Parameters) is available for generation the external parameter files with EXTPAR.
Please be aware, that the size of the domain of external data has to be larger then the size of the actual CCLM domain.
At least two further grid points at each of the four sides are required. It is recommended to chose the domain of the
external data set rather large, so that it is possible to change the size of the CCLM domain, with shifts of start_lon and start_lat,
etc. without creating new external data sets.
EXTPAR
Numerical Weather Prediction (NWP) models and Climate models require geographical localized datasets like the orographic height of the earth surface, the plant cover, the distribution of land and sea and, dependent on the schemes used, a variety of other external parameters.
The EXTPAR software system (EXTPAR - External Parameter for Numerical Weather Prediction and
Climate Application) is able to generate external parameters for the different models COSMO and ICON. The software can run on a UNIX or Linux systems where the raw data is stored. It allows operators (experienced users) running the scripts to create new external parameters controlled by user specifications like the model domain.
The following steps are performed for the generation of external parameters:
1. The target grid has to be specified, supported target grids are
• Rotated and non-rotated longitude-latitude grid (COSMO)
• Icosahedral Triangular grids (ICON) with optionally higher resolution in selected regions
('local zooming')
2. The different raw data sets are aggregated to the target grid considering all raw data elements
which are within the target grid element. If the target grid has a higher resolution than the input
grid on which the raw data is available either an interpolation is performed or the target grid
is filled with the nearest neighbor, but sub-grid scale statistical calculations (e.g. subgrid scale
variance of orographic height) are dismissed.
3. All the different external parameter sets have to be checked for consistency against each other.
In case of conflicts default values are set automatically. In the NetCDF output, information on the
input data and the processing software is given.
Latest Version: Extpar 5.0.0 (November 2018)
Source Code Administrator: Katie Osterried, C2SM (katherine.osterried@env.ethz.ch)
Language: Fortran 2008, python
External library requirements: zlib, HDF5, NetCDF