Systematic variations of Z–R-relationships from drop size distributions measured in northern Germany during seven years

Problems and artifacts related to small samples of measured distributions are discussed. These ground-based samples of rain drops are small per se and extremely small compared to what the radar samples aloft. After indicating rules for investigating such data, preliminary analyses and results are presented. Significant differences for all three locations (Hamburg, Berlin and Rostock) are only found for thunderstorms, as compared to warm- or cold-air advection and weak gradient type weather systems. An outlook suggests a three step procedure for extracting information from the radar image in real time. Information is needed on the relationship between radar echoes aloft and precipitation at ground level in order for radar data to be used in operational hydrological applications.