Electrification of Winter Minor Showerclouds (Shigure)

Abstract

Electrification of minor showerclouds which frequently appear in the Kyoto basin during the winter season (Shigure) has been investigated. Three models are presented in this paper, that is, the Gauss type developing model, the dissipating charge model, and the dissipating current model, assuming the two (main and subsidiary) current sources. The variation patterns of the ground electric fields calculated using these models are compared with the observed patterns, and it is found that the Gauss type developing model best fits the observed results, and that the subsidiary source current of 0.004A in the lower portion of the cloud coexists with the main source current of 0.02A in the upper portion of the cloud: two different charge generating mechanisms function in the minor showerclouds. The atmospheric temperature levels of these current sources are nearly same as the case of general thunderstorms, that is, the main current source works at -10°C level and the subsidiary current source does in the region near -5°C level. The associated typical charge distribution is estimated, that is, the positive charge of 3.3 Coul is located at 3.0km height, the negative charge of 4.5 Coul at 2.5km, and the positive charge of 1.0 Coul at 1.0km.