TROPICAL CYCLONES

27th May, 2021 Geography

GS PAPER I: Important Geophysical Phenomena such as earthquakes, Tsunami, Volcanic activity, cyclone etc.

Context: Cyclone Yaas weakens into deep depression.

Yaas' (pronounced as Yass) got its name from The word has its origin in the Persian language and means the flower jasmine in English.

Tropical cyclone

Tropical cyclone, also called typhoon or hurricane, an intense circular storm that originates over warm tropical oceans and is characterized by low atmospheric pressure, high winds, and heavy rain.
In the North Atlantic Ocean and the eastern North Pacific they are called hurricanes, and in the western North Pacific around the Philippines, Japan, and China the storms are referred to as typhoon
In the western South Pacific and Indian Ocean they are variously referred to as severe tropical cyclones, tropical cyclones, or simply cyclones.
Tropical cyclones rotate in a counterclockwise (or cyclonic) direction in the Northern Hemisphere and in a clockwise (or anticyclonic) direction in the Southern Hemisphere.

How do cyclones form?

The above figure shows how cyclones form. The green arrows show where warm air is rising. The red arrows indicate where cool air is sinking.

Tropical cyclones form only over warm ocean waters near the equator.
To form a cyclone, warm, moist air over the ocean rises upward from near the surface.
As this air moves up and away from the ocean surface, it leaves is less air near the surface. So basically as the warm air rises, it causes an area of lower air pressure below.
Air from surrounding areas with higher air pressure pushes in to the low pressure area. Then this new “cool” air becomes warm and moist and rises, too. And the cycle continues.
As the warmed, moist air rises and cools the water in the air forms clouds.
The whole system of clouds and wind spins and grows, fed by the ocean’s heat and water evaporating from the ocean surface.
As the storm system rotates faster and faster, an eye forms in the centre.
It is very calm and clear in the eye, with very low air pressure. Higher pressure air from above flows down into the eye.
When the winds in the rotating storm reach 39 mph (63 kmph), the storm is called a “tropical storm”.
And when the wind speeds reach 74 mph (119 kmph), the storm is officially a “tropical cyclone” or
Tropical cyclones usually weaken when they hit land, because they are no longer being “fed” by the energy from the warm ocean waters.
However, they often move far inland, dumping many centimeters of rain and causing lots of wind damage before they die out completely.

Cyclone Categories

Fig: The Saffir-Simpson Hurricane Scale

Is the Arabian Sea becoming cyclone-friendly ?

Annually, five cyclones on average form in the Bay of Bengal and the Arabian Sea combined.
Of these, four develop in the Bay of Bengal, which is warmer than the Arabian Sea.
In the Arabian Sea, cyclones typically develop over Lakshadweep area and largely traverse westwards, or away from India’s west coast.
The frequency and intensity of cyclones in the Arabian Sea have increased in recent years.
This is because of the rapid warming that has made the relatively cooler Arabian Sea (compared to the Bay of Bengal) a warm pool region that can actively support cyclone formation.
However, in recent years, meteorologists have observed that the Arabian Sea, too, has been warming. This is a phenomenon associated with global warming.

How are cyclones across the globe named?

The World Meteorological Organisation and UN Economic and Social Commission for Asia and Pacific (UN ESCAP) led Panel on Tropical Cyclones – a global body which also includes regional specialised meteorological centres (RSMC) as well as tropical cyclone warning centres -- prepares the names of the cyclones.
Indian Meteorological Department (IMD) is among six RSMCs in the world, is mandated to issue advisories and name tropical cyclones in the north Indian Ocean region.

Which countries name the cyclones?

The panel comprising 13 countries, including India, Bangladesh, Myanmar, Pakistan, the Maldives, Oman, Sri Lanka, Thailand, Iran, Qatar, Saudi Arabia, the United Arab Emirates and Yemen, name cyclones in the region.
In 2020, a new list of names was released that had 169 names of cyclones, having 13 suggested names each from 13 countries.

Why are the cyclones named?

The cyclones are named to identify the storms to send out warning notifications about their development.
As the technical names could be difficult for the common people to remember and spread awareness on, naming them gives an unique identifier to these cyclones and makes it easier for the media and various authorities to disseminate information on them.

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