I am curious what causes the charge build up in a cloud before lightning occurs. I have seen in a few places such as this, that the process is not fully understood. Is this some form of static electricity? Here are a few of my thoughts:
It seems that rain or ice particles occur are present in the clouds where this happens since thunderstorms are usually accompanied by rain.
These clouds tend to be cumulus or cumulonimbus clouds which are much taller than other types that are commonly encountered. Is the physical size of the cloud related to this type of buildup of charge or is it a result of the moisture content?
If the charge buildup is caused by static electricity which two surfaces are contacting to create the charge? Is this just rain and ice particles? Can it be something else? (I think I recall something about lightning storms without rain in the desert) Why do some clouds with lightning have rain and others do not if the rain drops are the source of the static?
Is there a minimum solid or liquid particle density needed for static electricity within a cloud?
Any thoughts would be interesting to hear!