Updated: Jul 2, 2020
What are cyclones?
In meteorology, a cyclone is a large scale air mass that rotates around a strong center of low atmospheric pressure. Cyclones are characterized by inward spiralling winds that rotate about a zone of low pressure. Cyclones can be the most intense storms on Earth.
What are the types of cyclones?
There are two types of cyclones: middle latitude cyclones and tropical cyclones.
1. Mid-latitude cyclones, sometimes called extratropical cyclones, form at the polar front when the temperature difference between two air masses is large. These air masses blow past each other in opposite directions. Coriolis Effect deflects winds to the right in the Northern Hemisphere, causing the winds to strike the polar front at an angle. Warm and cold fronts form next to each other. Most winter storms in the middle latitudes, including most of the United States and Europe, are caused by mid-latitude cyclones. The warm air at the cold front rises and creates a low pressure cell. Winds rush into the low pressure and create a rising column of air. The air twists, rotating counter-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. Since the rising air is moist, rain or snow falls. These two- to five-day storms can reach 1,000 to 2,500 km (625 to 1,600 miles) in diameter and produce winds up to 125 km (75 miles) per hour. Like tropical cyclones, they can cause extensive beach erosion and flooding. Mid-latitude cyclones are especially fierce in the mid-Atlantic and New England states where they are called nor’easters, because they come from the northeast. About 30 nor’easters strike the region each year.
2. Tropical cyclones arise in the tropical latitudes (between 10 degrees and 25 degrees N) in summer and autumn when sea surface temperature are 28 degrees C (82 degrees F) or higher. The warm seas create a large humid air mass. The warm air rises and forms a low pressure cell, known as a tropical depression. Thunderstorms materialize around the tropical depression. If the temperature reaches or exceeds 28 degrees C (82 degrees F) the air begins to rotate around the low pressure (counter-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere). As the air rises, water vapor condenses, releasing energy from latent heat. If wind shear is low, the storm builds into a hurricane within two to three days. Hurricanes are huge with high winds. The exception is the relatively calm eye of the storm where air is rising upward. Rainfall can be as high as 2.5 cm (1″) per hour, resulting in about 20 billion metric tons of water released daily in a hurricane. The release of latent heat generates enormous amounts of energy, nearly the total annual electrical power consumption of the United States from one storm.
Effects of cyclones on India
India is always hit by the tropical cyclones. The most effected states are Andhra Pradesh, Odisha, West Bengal and Tamil Nadu.
Over the years multiple cyclones have hit the east coast of the Indian subcontinent. The 1999 Odisha cyclone was the strongest storm to hit the Indian coast, as well as the strongest in the basin till date, with a minimum central pressure of 912 mbar (26.93 inHg) and Cyclone Nargis is the costliest cyclone with damages almost $12.9 billion. The 1970 Bhola Cyclone is the deadliest cyclone with almost 5 lakh people killed in the cyclone, mostly people from West Bengal on November 3, 1970.
Cyclones gain their energy from the heat and moisture generated from warm ocean surfaces. This year, the Bay of Bengal has posted record summer temperatures. Researchers have said this is a fall-out of global warming from fossil fuel emissions that has been heating up oceans. Only a handful of storms in the Arabian Sea and Bay of Bengal achieve the level of super cyclone, about one occurs every 10 years. According to a list maintained by Weather Underground, 26 of the 35 deadliest tropical cyclones recorded have occurred in the Bay of Bengal.
Super Cyclonic Storm Amphan was a powerful and deadly tropical cyclone that caused widespread damage in Eastern India, West Bengal to be specific, and also Bangladesh in May 2020. It was the strongest tropical cyclone to strike the Ganges Delta since Sidr of the 2007 season and the first super cyclonic storm to occur in the Bay of Bengal since the 1999 Odisha cyclone. Causing over US$13 billion of damage, Amphan is also the costliest cyclone ever recorded in the North Indian Ocean, surpassing the record held by Cyclone Nargis of 2008.
This cyclone was followed by another severe cyclonic storm called Nisarga. Nisarga was the strongest tropical cyclone to strike the Indian state of Maharashtra in the month of June since 1891. It was also the first cyclone impact to Mumbai since Cyclone Phyan of 2009. Nisarga originated as a depression in the Arabian Sea and moved generally northward. Making landfall in Maharashtra with winds of 110 km/h (68 mph), Nisarga became the strongest storm to strike the state in the month of June since 1891. Before Nisarga, only two depressions had struck Maharashtra in the month of June, in 1948 and 1980 respectively.
All of these recent cyclones are believed to be a result of global warming and the rising temperature of the planet. It is the time for us to conserve, protect and nurture our planet.