LAM activities in Austria in 2003 Yong WANG ZAMG, AUSTRIA 25th EWGLAM and 10th SRNWP meetings, Lisbon,

1. Operations In ZAMG, the spectral limited area model ALADIN is run on 2 Central European domains. ALADIN-LACE: 37 vertical levels and 12.2km horizontal resolution; coupled with ARPEGE. ALADIN-VIENNA: 37 vertical levels and 9.6km horizontal resolution,coupled with LACE.

Model domains ALADIN-LACEALADIN-VIENNA

Operational activities Installation of model version AL25t1 and AL25t2. Parallel run with Al25t2, and with different model topography. Installation of the model monitoring system. Computer upgrade from 20 to 24 CPUs. SGI origin 3400

2. Model intercomparison Hourly model predictions and observations of areal mean precipitation for area 9. Left: during the first (6-8 Aug. 2002) flood event. Right: the second (12-14 Aug. 2002) flood event.

3. Efforts on improvment on precipitation forecast over complex topography We have studied the MAP IOP2b case for identifying the problems of ALADIN precipitation forecast; for investigating the possibilities of improvment on the precipitation forecast over complex topography. This case is typical for heavy precipitation in the Alpine region. The ALADIN simulations with different resolutions, topographies and the tunings of the parameterization have been carried on.The performance of ALADIN over areas with different orographical charactristics and for the periods of weather evolution is also verified.

The main conclusion: Significant systematic deficiencies in model forecast can be still found even when model resolution is increased, increaing the resolution alone is insufficient to address the challenge of improving the forecast over complex topography. The model precipitation forecast was consistently too high on windward side and too low on the lee side of the mountain, and the overestimation depends much on the upslope gradient of the model topography. Mean orography in the model does improve the precipitation forecast, and doesn’t deteriorate the wind forecast. LBC plays a very important role in the precipitation forecast. The semi-prognostic test shows that ALADIN parameterised weaker convection than reality, and the model analysis doesn’t have any information of large-scale precipitation. Sensitivity tests show that the horizontal diffusion and the subgrid orographic gravity wave drag have a little impact on precipitation forecast for this case.

Horizontal cross section of precipitation forecasts,analysis and topography. Precipitation: 24h mean rate in mm/h from 06utc Forecast in red: large-scale; in black: convective. Observation in solid line: ETH in 25km resolution; in red: radar analysis.

Temporal evolution of the hourly areal mean precipitation forecast. Balck: radar analysis; red: Meso-NH; blue: coupled with forecast; green: coupled with the analysis. Time: 00utc utc

4. Verification ZAMG issues a bi-annual verification report which shows forecast errors of different models (ALADIN, ECMWF, statistical models) in comparison, over an extended period. It is available as pdf document from ZAMG’s homepage Verification statistics are the variable including T2m, 10m Wind, cloud amount, precipitation,Tmax and Tmin for the 9 major Austrian cities; and the forecast skill of 500hPa geopotential of ALADIN-VIENNA

Forecast skill