Hydrometeor classification with a C-band polarimetric radar

The scattering of electromagnetic energy by hydrometeors forms the basis of radar meteorology. Knowledge of hydrometeor types can be very important in particular applications. The occurrence of mixed-phase conditions, especially the melting of snow and ice, impacts on the accuracy of radar-based precipitation estimation and the discrimination of rain and hail is often very important in severe weather warning production. Other applications, described by Straka et al (2000), are linked to the estimation of latent heat release and the initialisation of hydrometeor species in numerical models. Fortunately, the type of hydrometeor responsible for the scattering of electromagnetic energy can produce significantly different characteristics of the returned radar signal, especially for multiparameter radars. This paper follows studies by Aydin et al. (1986), Straka and Zrnic (1993), Höller et al. (1994) and Vivekanandan et al. (2000) to further show that multiparameter radars have considerable potential to identify bulk hydrometeor types. The work was prompted in part by a primary application of the Bureau of Meteorology Research Centre (BMRC) Cband polarimetric radar (CPOL), described by Keenan et al. (1998), in the validation of the National Aeronautics and Space Administration (NASA) and National Space Development Agency of Japan (NASDA) Tropical Rainfall Measuring Mission (TRMM) products. The accuracy of TRMM algorithms is in part determined by the hydrometeor species and physical validation of these algorithms requires information on the vertical distribution of hydrometeors above the melting level, especially in the ‘mixed-phase’ region. This paper first describes the measurements undertaken by CPOL, summarises the microphysical classification procedure and then presents examples of the classification procedure in very different tropical and subtropical environments. This demonstrates the apparent robustness of the approach, a fact supported by routine use of the techniques in TRMM Ground Validation (GV) and the World Weather Research Programme Forecast Demonstration Project (Keenan et al. 2002) undertaken in Sydney, Australia. This Aust. Met. Mag. 52 (2003) 23-31