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

E. E. AVILA; R. G. PEREYRA; G. G. AGUIRRE VARELA; G. CARANTI

QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY

ROYAL METEOROLOGICAL SOCIETY

Año: 1999 vol. 125 p. 1669 - 1679

0035-9009

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 pm in diameter, impact velocities around 4 m s-', 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%100 pm in diameter, impact velocities around 4 m s-', 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%4 m s-', 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%Two different cloud-droplet spectra were used. One had more than 30% of the droplets with sizes greater than 13 pm, 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.the droplets with sizes greater than 13 pm, 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.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.-18 "C for the larger-droplet spectrum. These results show the importance of droplet sizes to thunderstorm charging.of droplet sizes to thunderstorm charging.