What causes charge buildup in a cloud before a lightning storm?

Question

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!

Answer 1

Charge separation occurs because of collision of particles. The surface of an ice pellet is not exactly pure H2O, it contains an excess of OH- ion (for crystal-boundary reasons that I do not understand). That's why ice is slippery.

So, if there is a mixture of sizes of ice pellets suspended in air (not unlikely, since we see hail from time to time), and (for instance) an updraft carries the lightest (smallest radius) particles UP past larger slower particles, we can confidently expect particles to collide.

The collision of a small and large particle makes a pointy spot (where the small particle is), and the surface charge in the OH- ions flows preferentially to that spot (because the negative charge repels). When that small ice particle detaches, it carries more negative charge and the large ice particle carries less.

So, a consequence of turbulent airflow and suspended water ice is net separation of charges inside a cloud. That charge separation generates the electricity we see as lightning.Charge Separation...

Answer 2

I found this lecture transcript helpful. It seems to have been one of a series given by Richard Feynman. http://www.feynmanlectures.caltech.edu/II_09.html

Answer 3

why ? are we getting areas of massive Rain Fall; Its because of sections of the Sky 'ionosphere' are being Blasted with extra Solar Bursts of Microwaves from the Sun; these said area's of High Electrical Charge' are Discharging Downwards to the Most Moist water vapour Clouds in the Stratosphere' which then become electrically Charged' which then in those SPECIFIC area's of Cloud' electric charge makes the these said clouds' collate even Larger amounts of water vapour' which then discharge there vast amounts of water vapor which then discharges as Cloud Bursts of Torrential RAIN' as it meets upward ascending Microwave energy from Mobile Phone Masts; in order to over come this problem' we need to link mobile phone masts in relays one to another with hard wired cables' its expensive' But if we do not;- then Nasty Extreme sporadic downpours of Rain will continue where there are a concentrated amount of Microwave Emitting Phone Masts;