| An outstanding problem in thunderstorm electrification is the exact method by which charge separation takes place, eventually creating lightning. Recent work on this subject has pointed to interactions between ice crystals as the dominant charging process, but the underlying method of charge separation in a single crystal is not well understood. This work started with a model originally proposed by Latham and Mason, where a temperature gradient creates a charge separation in an ice crystal due to the thermoelectric effect. Latham and Mason only considered the motion of ionic defects, and they were not able to solve their equations exactly. We created a generalized model, based on their original equations, simulating the motions of both ionic and Bjerrum defects (the latter discounted by Latham and Mason because they did not know them to be mobile). This model was solved numerically using finite element methods. The charge densities of each type of defect were calculated based on the temperature difference between both ends of the crystal. It was found that the Bjerrum defects dominated the process, creating electric fields that are orders of magnitude larger than those created by the ionic defects alone. This work is limited by uncertainty in a number of important parameters, including defect mobilities. |
