Q2-When does Lightning occur?
Lightning occurs when liquid and ice particles above the freezing level collide, and build up large electrical fields in the clouds. Once the electric fields get large enough a big spark of lightning occurs. Lightning occurs during a thunderstorms, and sometimes during volcanic eruptions, or dust storms. When there is a thunderstorm lightning exists . There are about 16 million lightning storms in the world every year.
http://ellerbruch.nmu.edu/classes/cs255w03/cs255students/awozniak/p6/LightningMain.html
http://en.wikipedia.org/wiki/Lightning