The condition for the formation of lightnings are storm clouds. Storm clouds could formed when a sufficient amount of heat, moisture and condensation nuclei are present. How storm clouds are formed and their connection with lightnings you will discover down below. You will also recognize how lightning strike is conduct.
Lightning is a natural electrical phenomenon, which is consist from a lightning and thunder. A conditions for the formation of lightnings are storm clouds which arise when a sufficient amount of moisture, condensation particles and heat are present. Lightnings in the storm clouds are formed by separating the charges. In the lower part of cloud is negative charge and in the upper part of cloud is positive charge. Due to vertical winds, which rise the water droplets which collide into the particle of ice in the cloud, the electrons charge separation occurs. This leads to excess electrons (negative charge) in the lower part of cloud.
To the formation of negative charge also contribute freezing of water droplets when they are rising. The rising part of freezing droplets have negative charge, other water droplets are raised by the wind into the positive part of the cloud. The process of lifting the water droplets and freezing the other particles, leads to the distribution of negative charge into lower part of the cloud and positive charge in the upper part of the cloud. Because of that in the lower and the upper part of the cloud appear sufficiently large electric field that generate the lightning. In addition to that, the negative charge on the lower part of the cloud from surface of the Earth deduct the electrons into a depth, so that only positive charge remains in the surface.
For the formation of lightning we just need a conductor. When the electric field between the cloud and the ground or within the cloud reach a critical value, the conductor become air itself. With such strong electric field ionization of the air appear, which means that the electrons are separated from atoms and molecules in the air and can travel freely. This state is called plasma. More often is the electric field in the cloud stronger than electric field between cloud and ground, so the majority of lightning happens within the cloud or between the clouds.
The lightning strike is a process
lightning is not instantaneous phenomenon, is a process that takes place in steps. First is formed the so called "lider" which start to spread from the lower (negative lightning) or the upper (positive lightning) part of cloud to the ground. Lider spread where air ionization occurs more frequently, and therefore the lider have unusual shape. Lider transmit weak violet light. When lider who is expanding from the cloud toward the ground looking for the way to the ground, the "streamer" which carries positive charge begin to rise up toward the cloud from the exposed parts of the ground. When lider and streamer meet, the conductive channel is established between the cloud and the ground. Through that channel electric charge from the cloud reach the ground. This is called lightning strike. When this happen the electric current that flow through the channel rapidly increase to a few 100kA. In addition to that, the air in the channel become very hot, which is seen as a flash. Heated air also expand very rapidly, which causing sonic shock wave that we hear as thunder and could be nearby the lightning destructive.
Usually all the electric current from the cloud doesn't run out of it, so we often see more lightning strikes after the first lightning strike. We called this strikes returning lightning strikes. For that strikes are significant that the electric current from the cloud flow through the same conduction channel , as in the first strike. Location of the returning lightning strike is usually very close to the the first strike, but could also occur up to several kilometers from the first strike. The time between the first strike and the returning strike is very short, usually only a few milliseconds.