First experiences of operational use of a dual-polarization weather radar in Finland

Nevvonen Ljubov, Saltikoff Elena First experiences of operational use of a dual-polarization weather radar in Finland. Many national weather services are taking dual-polarization radars in operational use, after three decades of use in research. In Finland, three systems are already running operationally, and the data are integrated as part of the national weather service infrastructure. This gives new possibilities for applications, but also sets new demands for measurement design. Our solution has been to alternate measurements optimized for dual-polarization with another set of measurements optimized for the best quality of Doppler velocity data. This paper describes the design of the new measurement schedule. Our experience after the first year of usage is illustrated with case studies in weather situations typical for Finnish climate. Configuring the measurements of the dual-polarization radar differs from the conventional radars. In the present type of signal processors used by FMI, time-domain processing has to be used for dual-polarization parameters. Thus, velocity de-aliasing with random phase and the most advanced clutter-cancellation methods are not available for this mode. FMI radar network consists of eight C-band Doppler radars, installed 1993-2005. Three oldest ones of these radars have been upgraded during years 2009-2010, and the new equipment is capable for dual-polarization measurements. This paper describes design and implementation of the new measurements for the dual-polarization radars, what are the needs and commitments guiding the design, and finally, what kind of information we get from the atmosphere using these measurements. The Finnish radar data are used in general weather analysis, weather services for aviation, road maintenance and media, as well as in some hydrological and NWP applications. The users' needs are different and sometimes contradictory. Based on the requirements and limitations, a measurement task schedule was designed to consist of twelve PPI scans and two RHI scans, to be repeated every 5, 7.5 or 15 minutes. The set includes scans in Dual-polarization mode and in conventional mode. Additionally "bird bath" measurements to calibrate the ZDR are made once every 15 minutes. Pictures of different parameters and products in the different weather cases show that dual polarization reveals properties of precipitation event not seen from conventional radar data. The first applications are there, but we forecast, that just like for Doppler data, only after years of routine measurements and active use of the existing tools, the most advanced new methods and needs will be found.