Ee. Avila et Gm. Caranti, A LABORATORY STUDY OF STATIC CHARGING BY FRACTURE IN ICE GROWING BY RIMMING, JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, 99(D5), 1994, pp. 10611-10620
Charge transfer by fracture between colliding ice particles is measure
d using a wind tunnel inside a cold room. The charges were recorded on
e by one and the mechanics of each collision was studied in detail. Th
e sign of the temperature gradient at a given point of impact on the s
urface influences the sign of the charge transfer. In this work we ext
end previous measurements to particles growing by riming. A cylinder g
rowing by riming in a wind tunnel was used as target for collisions at
5 m s-, with ice spheres of 100 mum in diameter in a wide range of te
mperatures. Charge transfers of either sign were also observed here an
d according to the ambient conditions, one of sign prevailed on averag
e. The transferences ranged from +/- 50 fC at higher temperatures incr
easing in magnitude to -80 fC at lower temperatures. There was ample e
vidence of fragmentation following most of the collisions. The influen
ce of the growth regime on the charging and the production of fragment
s were also studied. A physical model of the microscopical mechanism l
eading to the charging of the fragments is presented. The laboratory e
vidence, when applied to a thundercloud, suggests that the proposed me
chanism could operate in a wide range of conditions and even explain s
ome observations in situ related to the abundance of ice crystals. Com
parisons are made with other experiments and models on static charging
of ice.