Understanding the Characteristics of a Tropical Cyclone

Tropical cyclones, also known as cyclones, are referred to differently based on their location and strength. For instance, they are called 'hurricanes' in the North Atlantic Ocean and eastern North Pacific region and 'typhoons' in the western North Pacific region. In the Southern Pacific and the Indian Ocean, they are referred to as severe tropical cyclones or simply cyclones.

Tropical cyclones are compact, circular winds with a diameter of 320km. They swirl around a central region that has low atmospheric pressure. The wind rotation is primarily driven by the low-pressure center and the rotation of the Earth. Consequently, cyclones rotate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.

Contrary to popular belief, cyclones do not cause significant damage to underwater coral reefs. The subsequent sections will explain how these tropical cyclones form and the various factors that influence their development.

Formation of Tropical Cyclones

Tropical cyclones form in a narrow zone of low pressure that stretches across the equator. The winds on the north side of this zone, known as the north-east trades, blow from the north-east, while the winds on the southern side, known as the south-east trades, blow from the south-east.

The low-pressure area over the warm tropical ocean heats up, leading to the rise of air from this area in discrete parcels, causing the formation of thunderstorms. This results in a flow of very warm, moist, rapidly rising air, leading to the development of a centre of low pressure, or depression, at the surface.

Several conditions need to be 'right' at the same time for these cloud clusters to transform into a tropical cyclone. The most influential factors include a source of warm, moist air derived from tropical oceans with sea surface temperatures usually in excess of 27 °C; winds near the ocean surface blowing from different directions, causing air to rise and storm clouds to form; winds which do not vary greatly with height, allowing the storm clouds to rise vertically to high levels; and sufficient distance from the equator to provide spin or twist.

Occurrence of Tropical Cyclones

Tropical cyclones occur in various parts of the world and can drift far enough from the equator to move into areas dominated by westerly winds (found in the middle latitudes). These winds tend to reverse the direction of the tropical cyclone to an eastward path. As the tropical cyclone moves polewards, it picks up forward speed and may reach 30 m.p.h. or more. An average tropical cyclone can travel about 300 to 400 miles a day, or about 3,000 miles before it dies out.

Tropical cyclones also occur in various parts of the Pacific Ocean and can affect coastal regions of Mexico, south-east Asia, north-east Australia, and the South Pacific islands. Those that form in the Indian Ocean can affect India, Bangladesh, north-west Australia, some parts of East Africa, and Indian Ocean islands such as Mauritius and Madagascar.

Key Facts about Tropical Cyclones for UPSC Prelims

• Tropical cyclones are called by different names in different regions of the world:
  • Hurricane – Atlantic
  • Typhoon – Western Pacific and the South China Sea
  • Willy-Willies – Western Australia
  • Cyclone – Indian Ocean
• They originate and intensify over warm tropical oceans.
• A pre-existing weak low-pressure area or low-level-cyclonic circulation is essential for their occurrence.

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