Abstract : Q.3
Convective initiation in the Black Forest region in high-resolution MM5 simulations

Thomas Schwitalla, Günther Zängl, Hans-Stefan Bauer, Volker Wulfmeyer
schwital@uni-hohenheim.de
Institut of Physics and Meteorology, University of Hohenheim

Precipitation strongly affects many aspects of our economy and general livelihood. Therefore, efforts to improve quantitative precipitation forecast (QPF) have high priority in meteorological research. This is particularly challenging in the warm season where convective precipitation is more important. To improve QPF, a large research project, the priority program “Quantitative Precipitation Forecast” (SPP1167) was established in 2004 by the German Research Foundation (DFG). In this project many researchers from the modelling as well as the observing community participate in a coordinated manner. The field campaign of this priority program, COPS, will take place in summer 2007 in the Black Forest and the adjacent low mountain ranges, the Vosges and the Swabian Jura. To support the preparation of the measurement activities and to improve the physical understanding of summertime convection in this region, high-resolution numerical simulations have been conducted with the mesoscale model MM5. Another goal of our work is to find an optimal model configuration for quasi-operational high-resolution weather forecasts during the field phase.

Our work is based on systematic sensitivity experiments for 12 selected precipitation cases during the summer of 2005. They have been simulated with a nested configuration of the MM5 using a horizontal grid spacing down to 1 km. Comparison with observational data, including high-resolution raingauge measurements, indicates substantial differences in model skill among the various model configurations tested. To examine the regions of preferred convective initiation under controlled ambient conditions, we also conducted semi-idealized simulations with real topography but idealized large-scale conditions. One important initiation mechanism indicated by our results is flow convergence between different slope or valley wind circulations.