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Calculations of Electric Field Growth within a Cloud of Finite Dimensions

A. J. IllingworthPhysics Department, University of Manchester, Institute of Science and Technology, Manchester, England

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J. LathamPhysics Department, University of Manchester, Institute of Science and Technology, Manchester, England

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Abstract

A one-dimensional precipitative model of cloud electrification is outlined in which field growth results from the operation of either in inductive or non-inductive mechanism. The cloud is cylindrical, of finite dimensions, and charging is confined to a supercooled zone within which precipitation growth occurs. Account is taken of loss of negative charge arriving at the ground on precipitation and the storage of positive charge carried by the updraft to a level above the charging zone.

The most important conclusion is that previous models of cloud electrification, which have often been extremely elaborate, provide gross overestimates of the rate of field growth because they have assumed a cloud of infinite width. They also predict a “top-hat” distribution of field, which is shown to be quite unrealistic. The present calculations cast serious doubt on the capability of an inductive mechanism, by itself, to produce breakdown fields in the available time.

These calculations also indicate that 1) the retardation of field growth due to the effect of electrical forces on particle velocities is negligible; and that 2) the “lower positive charge” can be produced in the bases of clouds, in some circumstances, without having to invoke an additional charging mechanism.

Abstract

A one-dimensional precipitative model of cloud electrification is outlined in which field growth results from the operation of either in inductive or non-inductive mechanism. The cloud is cylindrical, of finite dimensions, and charging is confined to a supercooled zone within which precipitation growth occurs. Account is taken of loss of negative charge arriving at the ground on precipitation and the storage of positive charge carried by the updraft to a level above the charging zone.

The most important conclusion is that previous models of cloud electrification, which have often been extremely elaborate, provide gross overestimates of the rate of field growth because they have assumed a cloud of infinite width. They also predict a “top-hat” distribution of field, which is shown to be quite unrealistic. The present calculations cast serious doubt on the capability of an inductive mechanism, by itself, to produce breakdown fields in the available time.

These calculations also indicate that 1) the retardation of field growth due to the effect of electrical forces on particle velocities is negligible; and that 2) the “lower positive charge” can be produced in the bases of clouds, in some circumstances, without having to invoke an additional charging mechanism.

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