At the end of March and six months before the special observation period (SOP) of MAP, the nine partner consortium of HERA completed their studies regarding recent heavy precipitation cases in various parts of the Alpine region. The aims of the project and first results were outlined in MAP newsletter 8, 1998, pp. 16-17.
The bulk of the results is contained in 14 contributions to a special issue of the journal Meteorology and Atmospheric Physics (published by Springer, Vienna), which at present undergo the regular review procedure. Their appearance in print is scheduled for autumn this year.
Nine heavy precipitation episodes of the years 1992, 94, 95, 96 were selected for the construction of HERA radar composites combining data of up to twenty radars operated in Austria, France, Germany, and Switzerland. A grand total of 1104 half-hourly pictures have been produced spanning a period of 23 days. All pictures (GIF-format) and datafiles are collected in the user section of the MAP Data Centre (http:// map.ethz.ch/mm-doc/HERA.htm). Such composites will be provided in near-real-time during SOP for the guidance of wet-MAP-missions.
Systematic modelling studies were undertaken with both operational forecasting models (DM, LAMBO) and research versions (MEOS-NH, BOLAM). Besides a large number of detailed findings they revealed that the current horizontal resolution (10 to 15km) and micro-physical parametrizations are suitable for the simulation of events with dominant synoptic-scale forcing, but that the prediction of mainly convectively
driven storm systems calls for a higher spatial resolution, more advanced micro-physics and better initial data.
Furthermore, the first cross-validation on a daily basis of four operational forecasting models (used in France, Germany, Italy, and Switzerland) with a trans-national gridded observational dataset was carried out for selected time windows within the MAP seasons of 1995 and 96 (together 164 days). It points to systematic deficiencies in the operational models and in the observational database, which in themselves justify a concerted action such as the MAP-SOP.
A step forward regarding a more realistic description of the lifecycle of convective storms near the Alps during special campaigns is envisaged through the adoption of airborne Doppler radar techniques for cases over complex terrain. Novel retrieval algorithms were developed within HERA and will be applied during MAP-SOP.
Finally, different synthetic modelling studies with parameters derived from the selected cases were carried out to investigate some basic processes in isolation, viz. a half-analytical approach for the interaction of mature atmospheric fronts with idealized topography, the enhanced generation of convective systems north of the Alps during southerly flow, the combined effect of the Alpine arc-shape and moist low level jets on the concentration of precipitation into a comparatively small area, and serious implications for the predictability of heavy precipitation events due to the only coarse grain knowledge of upper-tropospheric perturbations on their way towards the Alps.
In summary, project HERA achieved a hitherto not available synthesis between quite diverse aspects of today’s measurement and simulation capabilities regarding heavy precipitation over terrain as complex as the Alps in the heart of Europe. Reliable observations and forecasts for the majority of severe events, which largely determine the spatio-temporal variability of the atmospheric branch of the hydrological cycle, are expected to be available in the near future. Techniques developed within project HERA will play a central role during the conduct of the MAP-SOP. The resulting datasets of unprecedented spatial and temporal resolution await an application regarding the construction of integrated hydro-meteorological warning systems, especially the areas of steep terrain.
