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A. K. Kamra

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A. K. Kamra

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A. K. Kamra

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A. K. Kamra

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A. K. Kamra

Abstract

The effect of the inclination of the electric field on the induction charging mechanism in thunderclouds is discussed. It is concluded that in contrast to the case when the electric field is assumed to be essentially vertical, under inclined electric fields the inductive charging process can impart either positive or negative charge to the cloud particles and that this may be an additional source of leakage currents.

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A. K. Kamra

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A. K. Kamra

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Theoretical expressions for the maximum electric field, the total and leakage currents, and the recovery time of the electric field have been developed for the failing precipitation mechanism of charge separation in thunderclouds. The derivations take into consideration the electrical forces acting on the precipitation and smaller particles. Quantitative dependence of the derived electrical parameters on the precipitation intensity and on the charge density of the precipitation particles has been studied in the case of the ice crystal-hailstone collision mechanism and the drop-splintering mechanism. Certain conditions for optimum efficiency of this charge separation process have been established and the minimum rates of precipitation required to generate different values of electric field have been calculated. It is inferred that precipitation particles of larger sizes will contribute more efficiently than the smaller ones in generating high electric fields. The results suggest lower and upper limits for the average charge density on precipitation particles so that the theoretical results might match the experimental data. Furthermore, it is shown that when the precipitation intensity and the charge density on the precipitation particles are high, the currents due to electrical forces acting on precipitation particles, which hitherto have been ignored, become comparable or even larger than the sum of currents due to conductivity in the thundercloud and due to the point discharge from the ground. It is concluded from a comparison of the results to the available data that failing precipitation may not he the dominant cause in separating charges in thunderclouds with intense electrification.

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A. K. Kamra

Abstract

Rates of growth of the electric field by the induction charging mechanism of charge generation in thunder-clouds have been calculated for various precipitation rates. It is concluded, in addition to point-discharge currents below the thundercloud and the conduction currents inside the thundercloud as leakage currents, that the electrical forces acting on precipitation and smaller size particles are important in determining the maximum electric field and the rate of charge separation in thunderclouds. The results have been qualitatively generalized for any charge generating mechanism based on the failing precipitation mechanism of charge separation in thunderclouds.

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A. K. Kamra and B. Vonnegut

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A laboratory experiment has been performed to study the relative effect of aerodynamic and electrical forces an small electrically conducting particles of radii 100–200 μ colliding with a particle of 2 mm radius suspended in an upward moving vertical air stream of a wind tunnel and placed in a vertical polarizing electric field. It has been observed, in a low electric field, that the smaller particles collide and move up with the air stream. However, as the electric field is increased, the smaller particles start coming down, after the collision, against the air stream. The electric field required for this change of direction for different particle sizes is higher for the larger angles of collision. When these results are applied to thunderstorms with high electric fields, it is shown that the electrical forces on the charged cloud particles must be taken into account in any consideration of the gravitational separation of charges. Our experimental results indicate that in high electric fields these electric forces can limit and even oppose the further separation of charges.

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A. K. Kamra and D. V. Ahire

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When a small isolated ice piece of conical shape is suspended with its apex facing down between two horizontal parallel electrodes and an electric field of 1 to 1.6 kV cm−1 is applied between them with the lower electrode at negative potential, a mist of fine monodisperse particles is observed for a fraction of a second from the apex of the ice piece. Charges on different ice pieces have been measured to be in the range of 10−9–10−8 C after the occurrence of smoke. The phenomenon has been simulated for some conditions that exist in melting layers of thunderstorms and it is proposed that ice graupel or hailstones falling in melting layers of electrified thunderstorms may produce the type of mist observed in our experiments. It is further suggested that the positively charged mist particles generated in this phenomenon may influence the cloud microphysics and might be responsible for the lower positive charge pockets sometimes reported in the bases of well-developed thunderstorms.

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