Thunderstorms are a significant part of the climate of the Northern Territory, and are most frequent about the northwest coast, near Darwin. In fact this area sees more days of thunderstorms than anywhere else in Australia and is recognised as having one of the highest rates of lightning strikes anywhere in the world. This region is the lightning capital of Australia. They are associated with cumulonimbus clouds which have a dark base and can reach heights of 20km or more, often with a bright anvil shaped top. Thunderstorms are more frequent in the tropical atmosphere due to the warm and humid environment and when severe, can produce hail, strong wind gusts and even tornadoes.
Thunder is the audible evidence of electrical activity in the clouds.
As clouds grow they accumulate massive amounts of electrical charge which can travel from one cloud to another or to the surface of the earth. This electrical charge travels as a very long electrical spark that is recognisable as lightning and can be several hundred million volts. The lightning causes a violent expansion of the air by heating it to as high as 30,000 degrees Celsius, which produces thunder. Approximately 40,000 thunderstorms occur throughout the world every day producing around 6,000 lightning strikes every minute, which maintains the balance of the electric potential between the earth and the atmosphere. The photograph depicted on this ticket was taken by Peter Jarver, one of Australia's foremost landscape photographers.