Contents

1. Development of a COSMO-Model Version for very high-resolution
2. Basic model set-up
3. Data assimilation
4. Operational Schedule

1. Development of a COSMO-Model Version for very high-resolution

In 2003, DWD started the Aktionsprogramm 2003, a temporary programme to improve the weather forecasting in Germany. One of the subprojects was the development of a model-based nowcasting system. For that, the COSMO-Model was used, but several extensions have been implemented, to suit the needs of such a system. The main new developments for the COSMO-Model are:

• Implementation of a 2 timelevel dynamical core based on Runge-Kutta methods. This allows the use of more accurate advection algorithms (5th order for horizontal advection), which is desirable for very high resolutions
• Deactivation of parameterization of high convection. The model will resolve this in the dynamics. A modified version of the parameterization for shallow convection is still kept in the model.
• The parameterization of cloud microphysics includes graupel.
• In the assimilation part, an algorithm for Latent Heat Nudging has been implemented to assimilate very high resolved radar data.

Since April 2007, the new version of the COSMO-Model is running operational in the COSMO-DE application of DWD. This application is described in more detail here.

2. Basic model set-up

The integration domain of COSMO-DE covers the whole of Germany, most part of the alps and some smaller parts of the neighboring states. It has 421x461 grid points in the horizontal and 50 vertical levels. The lowest level is 10 meters above ground, similar as in COSMO-EU. COSMO-DE uses the same rotation as COSMO-EU, with pollat=40.0^o and pollon=-170.0^o. The resolution used right now is 2.8 km (0.025^o). The rotated lat-lon coordinates of the lower left and the upper right corner of the integration domain are lon = -5.0^o, lat = -5.0^o and lon = 5.5^o, lat = 6.0^o, respectively. Figure 1 shows the integration domain with 421x461 grid points.

Fig. 1: Orography (height in m) of the operational domain of the COSMO-DE at DWD.

COSMO-DE is running 8 times a day (at 00, 03, 06, 09, 12, 15, 18, 21 UTC) for up to 24 hours. It runs on the same computer as COSMO-EU on 256 processors.

3. Data assimilation

Since April 2017 the KENDA technique is used as assimilation system for the atmospheric fields. In addition, the following external analyses are performed for the COSMO-DE.

• A sea surface temperature (SST) analysis (00 UTC),
• a snow depth analysis (00, 06, 12 and 18 UTC)

The latent heat nudging for assimilating radar data runs within the nudging of the COSMO-Model at 00, 03, 06, 09, 12, 15, 18, 21 UTC.

4. Operational schedule

Table 1: The operational suites for COSMO-DE at DWD in September 2017.

Suites	Pre-processing	Interpolation	COSMO-DE	Post-processing
Analysis	Snow Depth Sea Surface Temp	same as FCST	namelist YUSPECIF
Forecast (FCST)	-	namelist OUTPUT	namelist YUSPECIF