Context: Less than two weeks after a powerful cyclone passed through West Bengal on its way to Bangladesh, India is bracing to face another cyclone, this time on its western coast.
More on news:
- In strength and intensity, this would be much weaker than Cyclone Amphan.
- In fact, it is not even a full-fledged cyclone right now, just a ‘depression’ that is likely to intensify into a ‘deep depression’ , and eventually into a cyclone, after which it would be called Nisarga.
Path of Cyclone:
- It is headed towards the coastline of north Maharashtra and south Gujarat.
- By that time, it is likely to evolve into a Severe Cyclonic Storm, which is of strength 2 on a 1-to-5 of strength of cyclones that arise in the Indian Ocean.
Source: Indian Express
Strength of Cyclone:
- The strength of the cyclones are measured by the wind speeds they generate.
- At its strongest, Nisarga would be associated with wind speeds in the range 95-105 km per hour.
- Amphan, on the other hand, was classified as a super-cyclone, of category 5, though it had weakened to category 4, ‘Extremely Severe Cyclonic Storm’, ahead of its landfall, at which time the wind speeds were in excess of 180 kph.
- If the system does intensify into a cyclonic storm, some coastal districts of Maharashtra will come directly in line of its predicted path and heavy to very heavy rainfall is predicted in these areas until June 4.
- The southwest monsoon has already made an onset over Kerala.
- There is an associated depression lying parallel to the west coast which is intensifying and moving northwards along the coast which might delay the monsoon in upper western coast regions.
- Under such circumstances, the east-central and southeast regions of Arabian Sea are already experiencing rough weather conditions, which is likely to get intensified because of this cyclone.
Tropical cyclones are developed in the regions between the Tropics of Capricorn and Cancer.
They are caused by atmospheric disturbances around a low-pressure area distinguished by swift and often destructive air circulation.
- It requires warm ocean waters of at least 26.5°C [80°F]) throughout a sufficient depth, at least on the order of 50 m which is necessary to fuel the heat engine of the tropical cyclone.
- They need to form at least five degrees of latitude away from the equator because Coriolis force that is required for cyclones rotation is absent at equators.
- During a tropical cyclone, the Coriolis force deflects winds blowing towards the low-pressure center of the storm and creates circulation.
- They require low wind shear to form.
- Wind shear is the change in wind speed or direction with height in the atmosphere.
- High wind shear will slow spinning cyclones down and prevent them from lasting a long time.
- High relative humidity in the atmosphere up to a height of about 5,000 metres is required.
- Atmospheric instability that encourages the formation of massive vertical cumulus clouds due to condensation of rising moist air.
- In the China Sea and Pacific Ocean, they are known as typhoons;
- In the Caribbean Sea and Atlantic Ocean, they are known as hurricanes
- In north-western Australia they are known as willy-willies and
- In Indian Ocean they are known as tropical cyclones.
Reason for more Cyclones in Bay of Bengal than Arabian Sea
- Bay of Bengal has higher surface temperature in comparison and tropical cyclones need a higher temperature for cyclone genesis.
- In addition, the Bay receives higher rainfall and constant inflow of fresh water from the Ganga and Brahmaputra rivers.
- This means that the Bay’s surface water keeps getting refreshed, making it impossible for the warm water to mix with the cooler water below, making it ideal for a depression.
- Cyclones of low intensity also come from the foreign sources.
- Neighboring Pacific Ocean seas are more prone to cyclones.
- Typhoons originating near the Philippines, China, Thailand and Malaysia enter the Andaman Sea of Bay of Bengal after they weaken in their native regions.
- Coastal region of east is of low topography in comparison to Western areas with Ghats of high elevation.
- Most of the cyclones in the Arabian Sea are local. They collapse a little after making landfall as there is no back-up supply.
- Cyclones usually weaken if they encounter a large landmass.
- However, due to the lack of any such presence between the Pacific and the Bay, cyclonic winds easily move into the Bay of Bengal.
- Once here, the winds encounter the Western Ghats and the Himalayas, either becoming weak or getting blocked in the Bay, but never reaching the Arabian Sea.
image Source: Indian Express