Context: A cyclonic storm “Biporjoy” has developed over the east-central and adjoining southeast Arabian Sea, according to the India Meteorological Department (IMD).

• The system intensified from depression to deep depression and a cyclonic storm.

About

• ‘Biparjoy’ was suggested by Bangladesh and the word means ‘disaster’ or ‘calamity’ in Bengali.

• It is not rare for cyclones to develop in the Arabian Sea. There are fewer cyclones compared to the Bay of Bengal, but it is not uncommon.

• Between 1980–2019, Cyclone Gonu in June 2007 — the strongest cyclone in the Arabian Sea

• June is one of the favorable months for the formation of cyclones in the Arabian Sea.

How are Cyclones named?

• The naming of cyclones is done by countries on a rotational basis, following certain existing guidelines.

• Worldwide, there are six regional specialised meteorological centres (RSMCs) and five regional Tropical Cyclone Warning Centres (TCWCs) mandated for issuing advisories and naming of tropical cyclones.

• IMD is one of the six RSMCs to provide tropical cyclone and storm surge advisories to 13 member countries under the WMO/Economic and Social Commission for Asia-Pacific (ESCAP) Panel including Bangladesh, India, Iran, Maldives, Myanmar, Oman, Pakistan, Qatar, Saudi Arabia, Sri Lanka, Thailand, United Arab Emirates and Yemen.

Importance for naming tropical cyclones

• It helps to identify each individual tropical cyclone. 

• It facilitates disaster risk awareness, preparedness, management and reduction. 

• Local and international media become focused on the tropical cyclone.

• It removes confusion where there are multiple cyclonic systems over a region.

Worldwide terminology

Tropical storms are given different names around the world:

• hurricanes in the US and the Caribbean

• cyclones in South Asia

• typhoons in East Asia

• willy-willies in Australia

They all develop in the same way, have the same characteristics and are all tropical storms.

What is a Cyclone?

• A cyclone is any low-pressure area with winds spiralling inwards and is caused by atmospheric disturbances around a low-pressure area distinguished by swift and often destructive air circulation. 

• They originate over oceans in tropical areas and move over to the coastal areas bringing about large scale destruction due to violent winds (squalls)

• The air circulates inward in an anticlockwise direction in the Northern hemisphere and clockwise in the Southern hemisphere.

• The amount of pressure drop in the center and the rate at which it increases outwards gives the intensity of the cyclones and the strength of winds.

• The centre of a cyclone is a calm area. It is called the eye of the storm. The diameter of the eye varies from 10 to 30 km. It is a region free of clouds and has light winds.

• Around this calm and clear eye, there is a cloud region of about 150 km in size. In this region there are high-speed winds (150–250 km/h) and thick clouds with heavy rain. Away from this region the wind speed gradually decreases.

• A large cyclone is a violently rotating mass of air in the atmosphere, 10 to 15 km high. 

Formation of Cyclone

• Tropical storms usually form between 5° and 30° latitude.

• When the ocean surface waters reach at least 27°C due to solar heating, the warm air above the water rises quickly, causing an area of very low pressure.

• As the air rises quickly more warm moist air is drawn upwards from above the ocean creating strong winds.

• The rising warm air spirals upward and cools. The water vapour it carries condenses and forms cumulonimbus clouds.

• These cumulonimbus clouds form the eye wall of the storm.

• When tropical storms reach a land surface, they begin to lose their energy and die out. This is because they are no longer receiving heat energy and moisture from the ocean, which is needed to drive them.

Classifications of Cyclones

• Cyclones are classified as extra tropical cyclones (also called temperate cyclones); and tropical cyclones.

• Tropical cyclones are the progeny of ocean and atmosphere, powered by the heat from the sea; and driven by easterly trades and temperate westerlies, high planetary winds and their own fierce energy.

In India, cyclones are classified by

• Strength of associated winds,

• Storm surges

• Exceptional rainfall occurrences.

Major Factors Influencing Cyclone Formation

• Formation of Low Pressure: Cyclones form due to low-pressure systems over warm waters. The Bay of Bengal is slightly warmer, but the Arabian Sea is also getting warmer due to climate change, leading to an increase in cyclones.

• Coriolis Effect: In a depression or low-pressure situation, the air blows in an anticlockwise direction in the northern hemisphere, influenced by the Coriolis Effect.

Tropical storms and climate change

• Climate change could lead to tropical storms in more and different locations.

• Warmer seas could allow the storms to extend further north and south of the equator.

• Southwesterly winds associated with tropical cyclones over the Arabian Sea bring ample moisture onto the Indian subcontinent, enhancing the monsoon rainfall.

• Climate change may increase the number of cyclones with more intensity.

• Rising sea levels will make tropical storms more damaging, increasing coastal flooding.

• Cyclones in the Bay of Bengal can cause winds to turn around, inhibiting the northward progression of the monsoon winds over the region.