Dual-polarization weather radar observations of supercooled water and enhanced ice multiplication areas

Detection of supercooled water and its discrimination from ice precipitation is of great importance for mitigation of aviation hazards. Fuzzy logic polarimetric radar classification schemes have proven to be very used in distinguishing between different types of hydrometeors. Unfortunately, use the polarimetric classification schemes for detection of supercooled water droplets is difficult at best. Traditionally, polarimetric classification schemes are used either to detect supercooled drizzle droplets and/or signatures of rimed ice particles. Detection of supercooled water droplets is difficult because often the water droplets have smaller radar cross-sections than surrounding ice particles. Another approach of detecting polarimetric signatures of rimed particles, that act as proxy of supercooled water presence, is also not very successful because of lack of contrast between rimed and non-rimed ice particles.

It is known that supercooled water embedded in snowfall often manifests itself by enhanced secondary ice production. Increased concentrations of ice particles can be readily detected with a help of dual-polarization observations, for example by using differential reflectivity measurements. This approach allows detecting regions of supercooled water. In this paper we will present our study of using University of Helsinki dual-polarization C-band weather radar observations of supercooled water and enhanced ice multiplication areas of snow precipitation. This study is based on measurements carried out by the radar during winters 2005-2009. The radar observations are compared to vertically pointing Doppler spectral observations carried out by a University of Helsinki transportable C-band radar. Furthermore, WXREP reports, provided by pilots during landing and takeoff at Helsinki-Vantaa international airport, are used to verify radar observations of supercooled water areas.