Charge Distribution of Winter Thunderclouds

The charge distribution of winter thunderclouds that frequently visit coastal area of the Japan Sea, has been investigated. The mechanism of the charge separation is the same as that of summer ones and the separation is carried out most effectively around the temperature level of -10 C. In winter thunderclouds, the altitude of this level is about 2 km and the updraft velocity is restricted less than 4 m/s. Graupel particles, the principal bearers of negative charge, fall with the terminal velocity of 7 m/s and the negatively charged region in the cloud descends with ground-regarding velocity from 3 to 8 m/s, while positive charge born on ice crystals stays stationarily in the cloud. Thus, the period of dipole charge distribution in the clouds lasts for only several minutes and the period of positive monopole charge distribution predominates. This behavior of charge distribution in the cloud well explains the characteristic features of the winter lightning discharges.