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The effect of the cloud‐droplet spectrum on electrical‐charge transfer during individual ice‐ice collisions

1999; Wiley; Volume: 125; Issue: 557 Linguagem: Inglês

10.1002/qj.49712555709

1477-870X

Eldo E. Ávila, Rodolfo G. Pereyra, Guillermo G. Aguirre Varela, Giorgio M. Caranti,

Icing and De-icing Technologies

Abstract Experiments were conducted with a wind tunnel in a cold room, in order to investigate the influence of the cloud‐droplet spectrum on the charges transferred when individual ice spheres collided with a fixed artificial graupel pellet growing by riming. the experiments were carried out with ice spheres of about 100 μm in diameter, impact velocities around 4 m s −1 , temperatures between −10°C and −30°C and effective water contents representative of real clouds. Two different cloud‐droplet spectra were used. One had more than 30% of the droplets with sizes greater than 13 μm, and the other had more than 50% of the droplets greater than that. the new results show that the size distribution of the droplets is very important to the sign of electric charge transferred. the target graupel charged positively over all the temperature range covered when the smaller‐droplet spectrum was used, but negatively at temperatures below −18°C for the larger‐droplet spectrum. These results show the importance of droplet sizes to thunderstorm charging.