Open AccessCharge separation in low‐temperature ice cloud regions
Author(s) -
Ávila Eldo E.,
Bürgesser Rodrigo E.,
Castellano Nesvit E.,
Pereyra Rodolfo G.,
Saunders Clive P. R.
Publication year - 2011
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2010jd015475
Subject(s) - graupel , materials science , supercooling , lightning (connector) , particle (ecology) , liquid water content , ice crystals , atmospheric sciences , environmental science , meteorology , physics , geology , thermodynamics , cloud computing , power (physics) , oceanography , computer science , operating system
New laboratory measurements of graupel pellet charging due to collision with ice particles at low temperature are presented. The experiments were carried out in the temperature range −37°C to −47°C, with an impact velocity of 7 m s −1 and in the absence of supercooled liquid water. The graupel pellet was simulated with a previously rimed brass cylinder of 4 mm diameter, and the small ice particles were formed by natural freezing of supercooled water droplets at low temperature without seeding the cloud. The effective ice water content used in the experiments was between 0.25 and 0.33 g m −3 . Cloud particle samples show small ice particles with diameters up to 24 μ m. The results show that the sign of the charging current acquired by the graupel is predominantly negative, and its magnitude ranges from 0 to −150 pA; although there is a significant dispersion of data, a marked dependence on temperature is not observed. It is estimated that the magnitude of the charge transfer per collision is between 0.01 and 0.1 fC; the charging rate of a graupel pellet of 4 mm diameter then would be about 300 pC min −1 . Based on this experimental evidence, we suggest that the charging mechanism associated with graupel–frozen droplet collision and separation may be relevant in clouds whose internal temperatures are substantially lower than −37°C and could be the main generator for high‐altitude lightning.