In this section we consider only microphysical aspects of cloud electrification. The reader is referred to the in-depth review of lightning in this issue for further information.
In a recent review of thunderstorm electrification processes by
Saunders [1993], the importance of interactions between particles of
the ice phase, in the presence of liquid water droplets, in separating
electric charge in thunderstorms is emphasized. Numerical models based
on this charge mechanism show good agreement with observed electric fields
(Norville et al. [1991], Ziegler et al. [1991]), although further refinement
is still necessary. The modeling study by Ziegler showed best agreement
with observations when the temperature for sign reversal was -10
C,
instead of -21
C as advocated by Saunders et al. [1993] and others.
The resolution of which temperature to use for sign reversal is still
unresolved, and requires further research.