Rad4alp, The new Swiss Doppler polarimetric weather radar network: Data quality and first results

MeteoSwiss is currently engaged in the renewal of its operational weather radar network towards what it will constitute its 4th generation. The new radar systems are the 600C C-band polarimetric weather radars from Selex-Gematronik. At the moment, the three radars from the 3rd generation (Albis, Dole and Lema) have been replaced by the new sensors. Two new sensors will be added to the network: one in the Valais region and the other in the Grisons. The new sensors will greatly improve the coverage in the Alpine region, as well as adding redundancy in case of malfunction of one of the sensors.

The rough orography and the specific weather conditions (solid and mixed phase precipitation during the cold season, convective precipitation during the warmer months, orographic precipitation produced by shallow clouds all year round, etc.) in Switzerland constitute a challenge for an accurate quantitative precipitation estimation. Therefore, all the elements in the production chain, the scanning strategy, the system monitoring, the data processing, etc. have to be adapted and optimized. A brief overview of the specificities of the production chain is going to be provided in the extended abstract. Emphasis is going to be placed in the methods used, both at hardware and software level, to optimize the calibration and stability of the systems.

A fundamental tool to improve the quality of the radar products in the new generation is the use of polarimetry. In the new production chain, polarimetric data is used in three different areas: data quality monitoring and calibration, echo classification and precipitation estimation. A set of data quality monitoring tools, including differential reflectivity bias, differential phase system offset estimation, characteristic co-polar correlation coefficient in rain, noise measurements and reflectivity bias using self-consistency and Sun measurements and radar to radar comparison, have been already implemented to run in real time. The results of one year data evaluation are going to be presented in the conference. The polarimetric processing chain is currently being implemented and is going to be described in detail in the extended abstract. The first results of two of the outputs, hydrometeor classification and rainfall rate estimation will be analyzed. The hydrometeor classification will be based on a fuzzy logic algorithm using a combination of empirical and synthetic membership functions. The rainfall rate is going to be derived using a hybrid method combining the specific differential phase and the reflectivity data.