Tropical cyclones and local storms

TROPICAL CYCLONES AND STORMS

TROPICAL CYCLONE: 

• Tropical cyclones are generated in tropical areas of the ocean near the equator
• The winds generated move around a central eye
• Wind direction is counter-clockwise in the northern hemisphere and clockwise in the southern hemisphere
• They are low-pressure systems
• The low pressure calm centre of circulation is called the 'eye'
• The area around the eye with the fastest, most violent winds is called the 'eye wall'
• Bands of thunderstorms circulating outward from the eye are part of the evaporation-condensation cycle that feed the storm are called 'Rain Bands'

Stages of development of a tropical cyclone:

1. Tropical wave is a trough of low-pressure in the trade-wind easterlies
2. Tropical disturbance is a moving area of thunderstorms in the tropics that maintains its identity for twenty four hours or more
3. Tropical depression: is a tropical cyclone in which the maximum sustained surface winds is almost sixty kmph
4. Tropical storm is a tropical cyclone in which the maximum sustained surface wind speed is almost 120 kmph
5. A tropical cyclone has maximum sustained surface winds of almost 118 knph. It is also called a hurricane or typhoon in different parts of the world 

The three events essential for a cyclone to form are:

1. A continuing evaporation-condensation cycle of warm, humid ocean air
2. Patterns of wind characterized by converging winds at the surface and  strong uniform wind speeds at higher altitudes
3. A pressure gradient between the surface and high altitude

LOCAL STORMS:

1. Storms are a result of vertical circulation in the atmosphere
2. Heavier (cold ) air sinks and warm air (lighter) rises
3. Potential energy is converted to kinetic energy
4. Strong winds are intense when a thunderstorm is accompanied by heavy rain
5. Due to precipitation surrounding air cools down and is dragged down
6. Near ground level, the stream of air veers into a horizontal plane causing rain or hail stones into a sloping trajectory, sometimes at 45 degrees from the vertical
7. A local storm is produced by a cumulonimbus cloud and accompanied by lightening and thunder, usually with strong gusts wind, heavy rain and sometimes with hail

Destruction by Cyclones
The destruction caused by cyclones depends on its intensity, location and size. The effects of a cyclone can be divided into:

• Primary Hazards
• Secondary Hazards and
• Tertiary Hazards

Examples of primary hazards are:

1. Strong winds, heavy rains and storms
2. Abnormal rise in sea level at the coast
3. Submergence of low lying areas near the coast resulting in drowning  of humans, livestock, habitations, destroying vegetation and soil fertility
4. Very strong winds damage houses, trees and communication systems resulting in huge loss to life and property

Examples of secondary hazards are:

1. Floods, fire and freshwater flooding
2. Floods in rivers causing submergence of nearby inhabited areas
3. Erosion of valuable fertile agricultural land
4. Destruction of buildings
5. Strong winds in forest regions result in forest fires which spread the intensity of cyclonic winds

 Examples of tertiary hazards are:

1. Tertiary hazards include diseases caused due to stagnant water, water poisoning and increase in prices of goods and resources

 Sometimes all the hazards occur simultaneously because of which relief operations become difficult. . As the water level rises in the streets, transportation, communication, rescue operations and clean-up efforts extremely difficult.
Death toll due to cyclones is very high. Despite their devastating effects, cyclones of low intensity are beneficial because they bring rain to dry areas and move heat from the tropical regions.

Destruction due to local storms
Strong winds due to storms can damage and destroy vehicles, buildings, bridges and other outside objects turning loose objects into deadly flying projectiles.
Local storms damage the power supply to the local region
They also damage communication and hamper rescue and relief efforts
Cloud-to-ground frequently occurs during storms
They also damage vital local infrastructure