Dual polarization radar observations of anomalous wintertime thunderclouds in Japan

Dual-polarization radar observations of wintertime thunderclouds for the Sea of Japan are presented. The range-height-indicator (RHI) and plan-position-indicator (PPI) scans, respectively, reveal the height and horizontal distributions of ice particles, such as graupel and ice crystals. The overall shape of these ice particles is also confirmed on the ground. The ice crystals are, in general, found at high altitude near the cloud top, whereas the graupel is primarily seen near the center of clouds. The PPI display indicates a bandlike horizontal structure, and the lightning tends to occur around the bandlike gap where the ice crystals are, in advance, accumulated on the windward side of the preceding cloud. Simultaneous field mill observations indicate electric charge separation between these ice particles precipitating from the thunderclouds