Cyclone Study Notes for UPSC Exam

Cyclones for UPSC:  Cyclones are one of the most powerful and destructive forces of nature. Cyclone is the air mass that rotates around the centre of low atmospheric pressure, which typically rotates clockwise in the southern hemisphere and anticlockwise in the northern hemisphere. They are classified based on the intensity and the region where they form. 

The heat energy from the ocean drives the formation of cyclones over warm ocean waters that bring severe weather, which includes high winds, heavy rainfall and storm surges. For candidates preparing for UPSC prelims and mains, understanding cyclones is important to score well in topics like geography, environment, and disaster management. 

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How are Cyclones Formed?

Warm ocean surface temperatures—typically above 26°C (79°F)—allow cyclones to develop. An area of low pressure is produced when the warm water forces the air to rise. The major reasons for the formation of hurricanes are listed below.

• Warm temperature on the surface of the sea. 
• Atmospheric Pressure and Wind Pattern
• Disturbance in the preexisting low-level area of the ocean 
• Cyclones form over warm ocean waters near the equator, where the temperature is above 26 °C.
• Low pressure is created at the surface as warm air rises. The Coriolis effect causes the colder air to spiral inward as a result.

Types of Cyclones

There are two main types of hurricanes: tropical cyclones and extratropical cyclones. Tropical cyclones form in warm, tropical ocean waters, while extratropical cyclones form outside of tropical areas and are driven by different weather systems.

The cyclones are majorly divided into two types, i.e., tropical cyclones and extratropical cyclones. 

The tropical cyclones form in warm, tropical ocean waters. It develops between the regions of Tropics of Capricorn and Cancer. Tropical cyclones are classified by wind speeds (e.g., tropical depressions, storms, and hurricanes or typhoons).

The extratropical cyclones form outside of tropical areas and are driven by different weather systems. They generally form in temperate regions of high altitude. They bring themselves rain, storms, and sometimes snow.

Important Schemes for UPSC IAS Exam,

Tropical Cyclone

A tropical cyclone rotates around the low-pressure centre, producing strong winds and thunderstorms that produce heavy rains. The name of the tropical cyclone changes depending on their location; the common names are hurricanes in the Atlantic and Northeast Pacific region, typhoons in the Northwestern Pacific region and typhoons in the Indian Ocean and South Pacific region.

Formation of Tropical Cyclones

• Tropical cyclones form over warm waters (around 27°C or 81°F) and require low wind shear, high humidity, and atmospheric instability.
• Air rises rapidly, and the Earth's rotation causes it to spin cyclonically.
• Most storms form near the intertropical convergence zone.

Size & Impact of Tropical Cyclones

• The tropical cyclones cover a range from 100 to 2000 km in diameter.
• It causes damage through strong winds and heavy rainfalls. 

Extratropical Cyclones

Extratropical cyclones (also called mid-latitude cyclones or wave cyclones) are low-pressure systems that occur in the Earth's mid-latitudes (30° to 60° latitude).

These cyclones can produce a wide range of weather, from cloudiness and mild showers to severe gales, thunderstorms, blizzards, and tornadoes.

Extratropicals are formed in the extratropical regions through cyclogenesis or extratropical transition. These cyclones are classified as baroclinic. They form near upper-level jet streams, where upper-level divergence causes air pressure to drop, which results in strengthening the cyclone.

Cyclones in India

The Indian Subcontinent region is one of the affected regions in the world. The Indian Subcontinent has nearly 8041 kilometres of coastline, which is approximately 10% of the world's tropical cyclones. Out of these, the majority of their initial genesis was over the Bay of Bengal and striking the east coast of India. More cyclones occur in the Bay of Bengal than the Arabian Sea and the ratio is approximately 4:1.

As per the data released by the government, on the East and West coasts of India between 1891 and 1990, nearly 262 cyclones occurred (92 of these severe) in a 50-kilometre-wide strip above the East coast. Less severe cyclonic activity has been noticed on the West Coast, where 33 cyclones occurred in the same period, out of which 19 were severe. Tropical cyclones occur in the months of May-June and October-November. 

The criteria below has been formulated by the Indian Meteorological Department (IMD), which classifies the low pressure systems in the Bay of Bengal and the Arabian Sea on the basis of capacity to damage, which is adopted by the WMO where 1 knot is equal to 1.85 km per hour.

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