Dual Polarization Radar Observations of Thunderclouds in Winter Season.

The authors investigate the characteristics of thunderclouds associated with lightning phenomena in the winter season using the dual polarization Doppler radar of the Ministry of Construction known as the DND (Dobokuken-Nijuhenpa-Doppler) radar.This paper deals with the discrimination between different types of precipitation particles and presents the relationship between the movement of the particles and lightning processes.Our results suggest that the dual polarization observational mode, detecting both the horizontal radar reflectivity factor (Zn) and the differential reflectivity factor (ZDA), may discriminate between precipitation particles such as graupel or ice crystals, and that the observed radar echoes indicate a close relationship between the contact of these precipitation particles and the lightning process.Also, simultaneous field-mill observations suggest that graupel has negative charge while ice crystals have positive charge in thunderclouds.This electrical phenomenon is well described in terms of recent thunderstorm electrification theories at temperatures below -10°C.