Riming Electrification as a Charge Generation Mechanism in Thunderstorms

TLDR

Riming electrification has been investigated in cold‑room experiments that simulate thunderstorm conditions, with brief consideration of regional variations in thunderstorm characteristics. The authors aim to explain riming charge by proposing and discussing three distinct physical mechanisms that operate under varying temperature and cloud‑water‑content conditions. They examined how the ambient electric field and the freezing potential of rime droplets influence charge separation during riming, and used these insights to formulate the three proposed mechanisms. Experiments show that when ice crystals collide with supercooled droplets, riming probes acquire charges of ~33 fC per collision, with sign and magnitude strongly dependent on temperature and water content, sufficient to trigger lightning, while electric‑field and freezing‑potential effects are secondary.

Abstract

Riming electrification was studied in cold room experiments simulating thunderstorm conditions. When both ice crystals and supercooled droplets coexist in the experimental chamber, high electric charge occurs on the riming probes. Both the sign and magnitude of riming electrification are highly dependent on the temperature and cloud water content. Electric charge of the order of 10−4 esu (33 fC) is separated on riming with each ice crystal collision under conditions typical of the in-cloud environment of continental thunderstorms. This amount of charge is sufficient to produce the high electrification required for lightning discharge within reasonably short periods of time. The effect of the electrical field on charge separation during the riming and effect of the freezing potential of drops of rime also were examined. It appears that these effects play only a secondary role for charge separation in thunderstorms. Three different physical mechanisms of charge separation during riming are proposed and discussed to explain the riming charge under different conditions of temperature and cloud water content. Possible differences in the character of thunderstorms at various geographical locations are briefly considered.