The Collision-Coalescence Process



 The collision-coalescence
 process is an important
 mechanism in forming
 raindrops in warmer clouds
 (those with tops warmer than
 -15C = 5F).  In these warm
 clouds raindrops form
 exclusively by this process.
 Most tropical rain is formed in
 this way.  The collision-
 coalescence process is of
 relatively little importance in
 middle and high latitudes
 where, even in the summer,
 most precipitation begins high
 in the clouds where
 temperatures are well below
 freezing and the dominant
 mechanism is the so-called
 ice-crystal or Bergeron process.
 However falling raindrops in
 these clouds do grow by the
 collision-coalescence process.