Abstract
Measurements of electric charge on a riming probe (an ice-coated metal rod) were made during the collision of supercooled droplets and ice particles with the probe under various condition in a cold chamber. It was found that the most important factors in the electrification of the probe were temperature, temperature difference between the probe and ice particles, and rate of riming.
As the mechanism of the electrification, the following points were considered.
1. When the riming rate is high under favourable conditions, tearing off of fine structures of rime from the probe's surface is significant.
2. When temperature is relatively warm, e.g., warmer than about -10°C, tearing off of liquid-like film from the riming surface is effective.
In the light of these mechanisms, local positive space charge in the lower part of thunderclouds and field pattern of wave type were explained.
