Abstract : 3N.1
High resolution precipitation analysis and model validation over complex terrain

Benedikt Bica, Reinhold Steinacker
Department of Meteorology, University of Vienna

Precipitation diagnosis and prognostics over mountainous terrain still poses a challenge due to the complex influence of topography. Both stratiform and convective precipitation usually show patterns that can hardly be resolved by an observing network. Similarly, the analysis and modelling of precipitation fields is subject to limitations that arise from the steep gradients which might occur in precipitation fields over mountain regions.

In the proposed presentation, the VERA (Vienna Enhanced Resolution Analysis) method is applied to precipitation fields in order to assess its suitability for analysis and model validation. VERA is based on the variational principle and further allows the inclusion of supplemental knowledge of typical patterns of meteorological parameters (fingerprint) in the analysis process: in case there is a signal of the fingerprint field detected in the data it can be used for downscaling purposes.

The suitabilty of the fingerprint technique for improvement of the analysis quality is investigated in various tests. Furthermore, a fingerprint model for upslope rain is derived from a high resolution topographic data set. Together with two fingerprints for meridional and vertical precipitation gradients it is used for the analysis of the MAP IOPs 2b and 8. Finally, a MM5-field of the August 2005 flooding event in western Austria, Switzerland and Bavaria (19 - 24 August 2005) is assessed for local agreement with the observations in an inverse approach.

The results prove that the fingerprint technique may lead to a significant improvement of analysis quality under favourable preconditions and that it further facilitates an innovative approach for local model validation.