How is a cyclone formed?
Cyclone is a system of winds rotating inwards at a high speed with the area of low pressure in the middle. Also, read about categories of cyclones along with the major cyclones in 2019-20.
Tropical cyclones are formed only over warm ocean waters near the equator. When warm, moist air over the ocean rises upward from near the surface, a cyclone is formed. When the air rises up and away from the ocean surface, it creates an area of lower air pressure below. It causes the air from surrounding areas with higher pressure to move towards the low-pressure area which further leads to warming up of the air and causes it to rise above.
As the warm, moist air rises and cools the water in the air forms clouds. The complete system of clouds and wind spins and grows, along with the ocean's heat and water evaporating from the ocean surface.
As the wind system rotates with increasing speed, an eye gets formed in the middle. The centre of a cyclone is very calm and clear with very low air pressure. The difference of temperature between the warm, rising and the cooler environment causes the air to rise and become buoyant.
- When the winds speed is 39 mph (63 kmph), the storm is called a "tropical storm".
- Whereas when the wind speed reaches 74 mph (119 kmph), the storm is officially a "tropical cyclone" or hurricane.
Annually, around 70 to 90 cyclonic systems develop all over the globe. The Coriolis force causes the wind to spiral around a low-pressure area. As the presence of Coriolis force is negligible in the equatorial belt between 5 degrees north and 5 degrees south latitudes, hence cyclonic systems do not develop in this region.
Categories of Cyclone
Cyclones are categorized on the basis of the strength of the winds. Below mentioned are the different categories starting from level 1. The wind speed and damage potential of each category cyclones have also been mentioned.
Category 1: Wind Speed 74-95 mph
Damage: Minimal
Surge surface: 4-5 feet
Category 2: Wind Speed 96-110 mph
Damage: Moderate
Surge Surface: 6-8 feet
Category 3: Wind Speed 111-130 mph
Damage: Extensive
Surge surface: 9-12 feet
Category 4: Wind Speed 131-155 mph
Damage: Extreme
Surge surface: 13-18 feet
Category 5: Wind Speed >155 mph
Damage: Catastrophic
Surge surface: 19+ feet
Major Cyclones which hit Indian coasts recently
Cyclone Nivar which got built over the Bay of Bengal and heading towards the southern states and Union territory (UT) of Andhra Pradesh, Tamil Nadu and Puducherry. It is expected to make landfall on Wednesday causing heavy rainfalls.
Cyclone Amphan: It had hit Indian coasts in 2020, leading to major damage in West Bengal, along with the bordering areas.
Cyclone Nisarga: It was a severe cyclone which had hit the Indian subcontinent in less than 14 days of Amphan. It led to huge destruction in Maharashtra, causing a large number of fatalities. Cyclone Nisarga formed on June 1 and dissipated on June 4, becoming the strongest tropical cyclone to strike Maharashtra since 1891.
Cyclone Fani: It was a huge cyclone which caused major damage in Odisha, being the strongest tropical cyclone to hit the state since 1999. Odisha faced maximum vandalization among the states hit by the cyclone. Fani affected other states like West Bengal and Andhra Pradesh, as well as neighbouring countries like Bangladesh, Bhutan and Sri Lanka.
Cyclone Bulbul: It was another severe cyclone which impacted both West Bengal and Bangladesh. Bulbul was a tropical cyclone which began forming on November 5, 2019, and dissipated on November 11 and claimed 41 lives. Neighbouring countries like Myanmar and Thailand were also affected.
Cyclone Vayu: It was the strongest cyclone to hit the Saurashtra region of Gujarat since 1998. It was formed on June 10, 2019, dissipated on June 17 and claimed 8 lives in June 2019. Vayu is taken from the Sanskrit and Hindi word 'Vayu' meaning wind. It had affected more than 6.6 million lives in the northwestern parts of the country.
Cyclone Maha: It had impacted the states of Maharashtra, Gujarat and Kerala. It was formed on October 30, 2019, dissipated on November 7 as a severe cyclonic storm.
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