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R. F. Griffiths


Experiments are described in which ice samples resembling natural precipitation elements were exposed to an electric field of sufficient strength to produce corona at the extremities of the particles. Measurements were made of the residual charge QR left on the particles after the field had been turned off.

Values of QR lay typically in the range ∼0.1−0.5 nC at 1000 mb, falling roughly linearly with pressure. Possible applications of this process in thunderclouds are discussed.

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R. F. Griffiths and J. Latham


The calculations of Gay et al. of the terminal velocities of charged hydrormeteors in the presence of electric fields have formed the basis of computations of the charging current density J flowing through a thunder-cloud as a result of the operation of a precipitative mechanism of cloud electrification. Values of J were calculated for a range of values of field strength E, precipitation rate p O, precipitation content L, cloud water content C, charge distribution, total separated charge, and the fraction of the small particles that have undergone a charging event.

It is found that the estimated field required for the initiation of a lightning stroke (σ3.5 kV cm−1 can be achieved only over a narrow range of conditions. The ease with which precipitative mechanisms can produce breakdown fields is considerably increased, however, if account is taken of spatial inhomogenities in the field.

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