Cyclone Biparjoy

Context:

Developed in the Arabian Sea, cyclone Biparjoy,earlier expected to move towards the Pakistan coastline, has now changed its path and is heading towards the northern Gujarat coast with landfall expected.
According to India’s Regional Specialised Meteorological Centre (RSMC), the cyclone might cause storm surges of 2-3 metres in height, destruction of thatched houses, damage to pucca houses and roads, floodings, widespread damage to standing crops, plantations and orchards, and disruption of railways, powerlines and signalling systems in the northern and western coastal districts of Gujarat.
Cyclone Biparjoy, which is expected to generate wind speeds of 125-135 kmph with gusts reaching up to 150 kmph by the time it reaches land, is a tropical cyclone. The National Disaster Management Authority classifies cyclones broadly into two categories: extratropical cyclones and tropical cyclones.

What is a cyclone?

A cyclone is a large-scale system of air that rotates around the centre of a low-pressure area. It is usually accompanied by violent storms and bad weather. As per NDMA, a cyclone is characterised by inward spiralling winds that rotate anticlockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.

Also known as mid-latitude cyclones, extratropical cyclones are those which occur outside of the tropic. They have “cold air at their core, and derive their energy from the release of potential energy when cold and warm air masses interact”, according to the US National Oceanic and Atmospheric Administration (NOAA). It added that such cyclones always have one or more fronts — a weather system that is the boundary between two different types of air masses. One is represented by warm air and the other by cold air — connected to them, and can occur over land or ocean.

Tropical cyclones are those which develop in the regions between the Tropics of Capricornand Cancer. They are the most devastating storms on Earth. Such cyclones develop when “thunderstorm activity starts building close to the centre of circulation, and the strongest winds and rain are no longer in a band far from the centre,” NOAA noted. The core of the storm turns warm, and the cyclone gets most of its energy from the “latent heat” released when water vapour that has evaporated from warm ocean waters condenses into liquid water, the agency added. Moreover, warm fronts or cold fronts aren’t associated with tropical cyclones.
Tropical cyclones have different names depending on their location and strength. For instance, they are known as hurricanes in the Caribbean Sea, the Gulf of Mexico, the North Atlantic Ocean and the eastern and central North Pacific Ocean. In the western North Pacific, they are called typhoons.

What is the “landfall” of a cyclone?

Simply put, landfallis the event of a tropical cyclone coming onto land after being over water. As per the IMD, a tropical cyclone is said to have made a landfall when the center of the storm – or its eye – moves over the coast.
Crucially a landfall should not be confused with a ‘direct hit’, which refers to a situation where the core of high winds (or eyewall) comes onshore but the centre of the storm may stay remain offshore. As per the US’s National Oceanic and Atmospheric Administration (NOAA), because the strongest winds in a tropical cyclone are not located precisely at the centre, it is possible for a cyclone’s strongest winds to be experienced over land even if landfall does not occur.

What is the damage caused by a cyclone’s landfall?

The damage caused by the landfall will depend on the severity of the cyclone – marked by the speed of its winds. For Cyclone Biparjoy, classified by the IMD as a “very severe cyclonic storm”, the impact may include extensive damage to kutcha houses, partial disruption of power and communication lines, minor disruption of rail and road traffic, potential threat from flying debris and flooding of escape
The factors behind this kind of damage include extremely strong winds, heavy rainfall and the storm surge which cause devastating floods in the coast.

How long does a landfall last?

Landfalls can last for a few hours, with their exact duration depending on the speed of the winds and the size of the storm system. Cyclone Biparjoy’s land process is expected to last around five to six hours, with the cyclone almost completely dissipating over approximately the next 24 hours.
Cyclones lose their intensity once they move over land because of sharp reduction of moisture supply and increase in surface friction. This means that while landfalls are often the most devastating moments of cyclones, they also mark the beginning of its end.

Source: Indian express