On clear days and nights there is a slow, steady, nearly uniform flow of electricity from the surface of the negatively charged earth and oceans to about 50 km up into the positively charged atmosphere. Where there are no clouds, between the earth and the 50 kilometer elevation, the electric field may reach values as high as 100 volts per meter. In thunderclouds the electric field may be much higher.
Solar energy is the ultimate source for creating lightning.
Warmth from the sun's radiant energy is responsible for convection of air, snow, rain, and hail within clouds. Free charges created in the upper atmosphere by cosmic rays also play a role in the detailed behavior of lightning. There are major differences between summer and winter thunderheads, and between those over Florida, New Mexico, South America and Japan. For the most common type of lightning, negative cloud to ground, there is a strong negative region in the lower section of the cloud. The base and top of the cloud may also have scattered positive regions.