- Introduce by defining thunderstrorms
- Explain the origin via the formation of cumulonimbus clouds
- Describe the 3 stage cycle of thunderstorm
- Conclude appropriately
Thunderstorms are local storms characterised by swift upward movement of air and heavy rainfall with cloud thunder and lightning. These are associated with the cumulonimbus clouds. Atmospheric instability, updraft of potentially unstable air, abundant supply of warm and moist air, thick clouds. etc. are the factors which favour the development of thunderstorms
Origin and development of Thunderstorms
Thunderstorms are formed by the uplifting of warm and humid air. There are many factors that lead to the uplifting of air, like solar heating, low pressure troughs, meeting of two different air streams meet or when air is forced uphill.
When humid air is lifted, it gets cooled and the moisture in the air condenses to form cloud. Upon further uplifting, the cloud will extend higher. Water droplets in the cloud continue to grow in size. As the cloud extends further upward, ice crystals may form because of low temperature there. A cumulonimbus cloud results when it grows to a height of 10 to 20 kilometres. Thunderstorms are produced by cumulonimbus clouds.
Example: Air mass thunderstorms normally develop in late afternoon hours when surface heating produces the maximum number of convection currents in the atmosphere.
Most thunderstorms developed by a cycle that has three stages:
- Cumulus stage
- Ground is significantly heated due to solar insolation.
- A low pressure starts to establish due to intense upliftment of an air parcel (convention).
- Air from the surroundings start to rush in to fill the low pressure.
- Intense convection of moist hot air builds up a towering cumulonimbus cloud.
- Mature stage
- Characterized by intense updraft of rising warm air, which causes the clouds to grow bigger and rise to greater height, as high as tropopause.
- Later, downdraft brings down to earth the cool air and rain.
- The incoming of thunderstorm is indicated by violent gust of wind. This wind is due to the intense downdraft.
- The updraft and downdraft determine the path of the thunderstorm. Most of the time, the path is erratic.
- Dissipating stage
- When the clouds extend to heights where sub-zero temperature prevails, hails are formed and they come down as hailstorm. Intense precipitation occurs.
- In a matter of few minutes, the storm dissipates and clear weather starts to prevail.
Thunderstorms have wide-ranging effects on human life, including electrocution, shock, and even worse, deaths. However they have some positive effects too. For instance, lightning helps produce ozone through electrical excitation of oxygen molecules. It also creates nitrate from nitrogen, which is essential for plants to grow and thrive on earth.
Subjects : Geography – Physical