Why are cyclone fomed ?

This is some content from our class 7 study material:

What are cyclones?

Water on the surface of the Earth absorbs heat and changes to vapour. As water vapour moves up higher in the atmosphere, it carries this heat along with it. The higher regions of the atmosphere are cooler. This condenses the water vapour into water drops.

When vapour cools down, it releases the absorbed heat into the atmosphere. The heat thus released warms up the air, which once again causes it to rise up. A low-pressure area is thus formed and the air from the surrounding areas rushes in. This sequence of events is repeated continuously.

Thus, this cycle is the result of the formation of a very low-pressure system with high wind speeds revolving around it. This weather phenomenon is known as a Cyclone.

The low-pressure centre of a cyclone is known as the eye of the cyclone. It is very calm i.e. the centre of the storm is actually free from storm and rain!

More about cyclones

  • The height of a cyclone varies from l0 km to 15 km

  • Cyclone is a whirl of a large mass of air in the atmosphere

  • The size of the eye of a cyclone may extend from 30 km to 65 km in diameter

  • The large mass of air containing clouds in a cyclone may extend up to 150 km with wind speeds of about 150 km to 250 km per hour

  • Cyclones are called hurricanes in the American continent and typhoons in Philippines and Japan.

Factors that affect the generation of cyclones

  • Humidity

  • Temperature

  • Wind speeds

  • Wind direction

Why are cyclones destructive?

The characteristic features that make cyclones destructive are

  • High wind speeds: Wind speeds ranging from 150 km to 250 km per hour are capable of destroying houses, crops, trees, electric and communication lines.

  • Low pressure: High wind speeds and very low pressure conditions, especially around the eye of the cyclone, cause the ocean water to rise as high as 3 to 12 meters. This rise in the ocean water submerges the low-lying areas near the shore, causing damage to life and property along the shoreline. The fertility of the soil also gets affected due to the saline water of the oceans.

  • Heavy rain: Cyclones are accompanied by heavy rains. If rains continue for longer periods, it causes floods.

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Cyclones are formed from simple thunderstorms. However, these thunderstorms can only grow to cyclone strength with cooperation from both the ocean and the atmosphere. First of all, the ocean water itself must be warmer than 26.5 degrees Celsius (81F). The heat and moisture from this warm water is ultimately the source of energy for cyclones. Cyclones will weaken rapidly when they travel over land or colder ocean waters -- locations where their heat and/or moisture sources do not exist.

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Cyclogenesis is the development or strengthening of cyclonic circulation in the atmosphere (a low pressure area).Cyclogenesis is an umbrella term for several different processes, all of which result in the development of some sort of cyclone. It can occur at various scales, from the microscale to the synoptic scale.

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