Wednesday, April 15, 2009


Lightning is an atmospheric discharge of electricity usually accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms.[1] In the atmospheric electrical discharge, a leader of a bolt of lightning can travel at speeds of 60,000 m/s (220,000 km/h), and can reach temperatures approaching 30,000 °C (54,000 °F), hot enough to fuse silica sand into glass channels known as fulgurites which are normally hollow and can extend some distance into the ground.[2][3] There are some 16 million lightning storms in the world every year.[4]
Lightning can also occur within the ash clouds from volcanic eruptions, or can be caused by violent forest fires which generate sufficient dust to create a static charge.[1][5]
How lightning initially forms is still a matter of debate:[6] Scientists have studied root causes ranging from atmospheric perturbations (wind, humidity, friction, and atmospheric pressure) to the impact of solar wind and accumulation of charged solar particles.[4] Ice inside a cloud is thought to be a key element in lightning development, and may cause a forcible separation of positive and negative charges within the cloud, thus assisting in the formation of lightning.[4]