The mechanism by which small particles in the clouds are removed by the formation
of raindrops; this is a different mechanism from wash out which is a process which
occurs below cloud level. Both the terms rain out and
wash out have not always been used in accordance with these definitions. For clarity they
should be replaced by the terms, in-cloud
scavenging and below-cloud
scavenging, respectively.
Source:
PAC, 1990, 62, 2167
(Glossary of atmospheric chemistry terms (Recommendations 1990))
on page 2209