Explain the types of Lighning Strokes with neat sketch.
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Answer:
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Explanation:
Lightning Stroke
Definition: Lightning stroke is the direct discharge of an electrical charge between the atmosphere and the object of earth. It is a sudden flow of electric charge between the electrical charge area of a cloud also called intra-cloud and another cloud called (CC lightning) or between the charged cloud and the ground (CG lightning).Mechanism of the Lightning Discharge
In the atmosphere, the positive, as well as the negative ions in the air, attach themselves to the small dust particles. The water drops present in the air also get charged because of polarisation by induction. These charged particles and water drops charged the clouds. The positive ions are collected in the upper region, and the negative ions are collected in the lower region of the cloud because of their mass.
When the charge cloud passes over the earth, it induces an opposite charge in the earth below. The potential difference in the cloud is not much greater than that at the earth’s surface, the discharge originates in the clouds. The potential gradient of the clouds is not uniform, and it is of the order of 10 – 30 KV/cm in any part of the cloud. The initial discharge which is also called pilot discharge or pilot leader moves slowly towards it from the earth.
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The first discharge moves to earth in steps of about 50 meters each and is, therefore, termed the stepped leader. The pilot leader carries a charge with it, and the potential gradient at its tips is very high. It ionises the air and provides a path or channel for the pilot leader. The channel also becomes charged. The pilot leader carries secondary steamer which branches out from it.
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When the pilot steamer reaches near the earth, the electric field intensity increases and due to this, the charges of an opposite polarity in the form of a short steam rises from the earth to meet the tip of downward leader. When a contact is made between the pilot leader and the short upward steamer, a return streamer travel from the earth to cloud along the ionised channel formed by the pilot leader. The return steamer moves very fast and produces the well known, intensely luminous lightning flash.
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The potential of the portion of the cloud from where the discharge originated is lowered by the passage of the charge through the ionised channel to the earth. But the other portion of the clouds remains charged. Therefore, a high potential develops between the original charge centre and another charge centre in the clouds.