High-Resolution Quantitative Precipitation Estimation and Nowcast Using Dual-Polarization Radar Network

Among various precipitation measurement sensors, radar is unique in the sense it is capable of providing observations over a wide area in a relatively short time span and also keeping track space time variability including storm motion and evolution in 4 dimensions (3D+time). In addition, polarization diversity has been shown to be very useful to characterize precipitation microphysics through identification of raindrop size distribution and different hydrometeor phases. Currently, ground-based dual-polarization radar systems form the cornerstones of national severe weather warning and forecasting infrastructure in many countries. In addition to regional and/or national forecast and warning operations, dual-polarization radars have also been used to validate space-based precipitation retrieval algorithms and products. Ground radars are a key component in the Global Precipitation Measurement (GPM) mission ground validation field campaigns. The operational dual-polarization radars in the U.S. are mostly S band systems whereas in Europe are mostly C band systems. In addition, a third class of systems is emerging in urban regions where networks of X band systems are being deployed operationally. Typical examples include the X-band networks planned or already deployed in big cities such as Dallas-Fort Worth (DFW) and Tokyo. These X band radar networks are developing their own operational domain for urban weather disaster detection and mitigation. At the same time, soft infrastructure in terms of user specified products are emerging in these systems.

Numerous studies in the past have shown that the microphysical information from dual-polarization radars is supposed to improve the quantitative retrieval of rainfall, but it has been very hard to demonstrate this in practice, due to lots of practical engineering problems. However the short range, high resolution, low level observations with X band radar network have shown that many of these limitation can be overcome. This paper will present some of the innovative uses of the DFW operational dual-polarization radar networks for research and operational demonstration purposes, with of a focus on quantitative precipitation estimation and nowcast. The techniques integrating different data sources at multiple space-time scales are detailed for generating real-time high-resolution high-quality precipitation products. This paper also discusses the rationale and opportunities of using ground based dual-polarization radars in validation of precipitation retrievals from space radar, through detailed comparisons between GPM Dual-frequency Precipitation Radar (DPR) and ground radar observations, particularly the instantaneous precipitation rate products.