Tropical Cyclones

The atmospheric pressure causes air to travel from a high-pressure to a low-pressure state, causing the air to move. It also controls whether the air will rise or fall in temperature. When the wind moves overseas and over the ocean, due to moisture condensation, it generates latent heat. A tropical cyclone is also known as a hurricane and is like a heat engine as it drives energy from the release of this latent heat.

Tropical Cyclones in India

• Tropical cyclones or typhoons are intense low-pressure areas that originate from the warm tropical ocean and are confined only between 30° N and 30° S latitudes as the wind blows comparatively at a high velocity
• Tropical cyclones can extend up to 500-1,000 km horizontally and about 12 – 14 km vertically from the surface
• Favourable conditions for the formation and intensification of tropical storms are:
  • large sea surface with temperature higher than 27° C
  • presence of the Coriolis force
  • small variations in the vertical wind speed
  • a pre-existing weak low-pressure area or low-level-cyclonic circulation, and 
  • upper divergence above the sea level system

Reasons for the Emergence of the Tropical Cyclone

• A regular and large supply of warm air that ultimately releases ample latent heat
• In case an unstable condition forms that generate disturbances in and around the troposphere, it can lead to cyclone development
• Finally, if the vertical transport of the latent heat is disturbed due to insufficient or absence of a vertical wind wedge can contribute to a cyclone development

Structure of the Tropical Cyclone

• The structure of the tropical cyclone can be categorised as massive pressure gradients
• The cyclone’s centre is generally warm and low-pressure, also known as the eye of the storm
• Since the isobars are placed close to each other, they reflect high-pressure gradients
• Generally, it remains between 14-17 mb/100 km, at times, but it can even rise to 60mb/100km

Spatial-Temporal Distribution of the Tropical Cyclone

• Due to its Peninsular shape, the tropical cyclones in India also originate in the Arabian Sea in the west and the Bay of Bengal in the east
• During monsoons, the tropical cyclone develops between 10°-15° north latitudes
• In the Bay of Bengal, cyclones are most likely to originate in October and November

Surge: A surge is generated due to the interaction of air, sea, and land. The cyclone provides the driving force in the form of very high horizontal pressure-gradient and very strong surface winds. The seawater flows across the coast along with strong winds and heavy downpours.

Consequences of Tropical Cyclones:

• The first consequence of Tropical Cyclones in India is that as the distance increases between the Bay of Bengal and the Arabian Sea, the force of the cyclone decreases
• Therefore, the coastal areas are most likely to suffer severe cyclonic storms at an average velocity of 180 km/h
• In this case, the sea level rises which is termed a Storm Surge
• This gives rise to unwanted circumstances such as disturbance in human settlements, crop damage, impact on agriculture, and destruction of buildings

Extra-Tropical Cyclones 

• Systems developing in the mid and high latitude, beyond the tropics are known as extra tropical cyclones
• They form along the polar front
• in the northern hemisphere, warm air blows from the south and cold air from the north, when the pressure drops along the front, the warm air moves northwards and the cold air moves southwards creating an anticlockwise cyclonic circulation
• it leads to a well-developed extra tropical cyclone, with a warm front and a cold front

Difference between an Extra-Tropical Cyclone and Tropical Cyclone

• Extra tropical cyclones have a clear frontal system which is not present in the tropical cyclones and cover a larger area 
• It affects a much larger area as compared to the tropical cyclone
• wind velocity in a tropical cyclone is much higher and it is more destructive
• Extra-tropical cyclones move from west to east but tropical cyclones move from east to west

Conclusion

The general circulation of the atmosphere sets in motion the ocean water circulation which ultimately influences the earth’s climate and also affects the oceans and creates cyclones. Tropical cyclones originate and intensify over warm tropical oceans. They are known as cyclones in the Indian Ocean, hurricanes in the Atlantic, typhoons in the Western Pacific and South China Sea, and Willy-willies in the Western Australia.