CYCLONES
1. Context
The severe cyclonic storm Montha began its landfall near Kakinada in Andhra Pradesh around 7 p.m. on Tuesday, the India Meteorological Department (IMD) said.
2. What is a Cyclone
- A cyclone is a low-pressure system that forms over warm waters. Essentially, it is a system of high-speed winds rotating around a low-pressure area, with the winds blowing counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.
- According to the World Meteorological Organization, “Tropical cyclones are one of the biggest threats to life and property even in the formative stages of their development.
- Cyclonic winds move across nearly all regions of the Earth except the equatorial belt and are generally associated with rain or snow
- They include several different hazards that can individually cause significant impacts on life and property, such as storm surge, flooding, extreme winds, tornadoes and lighting.
- Combined, these hazards interact with one another and substantially increase the potential for loss of life and material damage.”
- Cyclones occur chiefly in the middle and high latitude belts of both hemispheres. In the Southern Hemisphere, where most of the terrestrial surface is covered by the oceans, cyclones are distributed in a relatively uniform manner through various longitudes
- Characteristically, they form in latitudes 30° to 40° S and move in a generally southeasterly direction, reaching maturity in latitudes around 60°.
- Cyclones that form closer to the Equator (i.e., at latitudes 10° to 25° north and south over the oceans) differ somewhat in character from the extratropical variety. Such wind systems, known as tropical cyclones, are much smaller in diameter.
- Whereas extratropical cyclones range from nearly 1,000 to 4,000 km (620 to 2,500 miles) across, tropical cyclones typically measure only about 100 to over 1,000 km in diameter.
PC: Brittanica
3. Types of cyclones
3.1.Tropical Cyclones
Cyclones developed in the tropics region (the majority confined to 100– 300 N and S of the equator) are called tropical cyclones.
- tropical cyclones have a thermal origin, and they develop over tropical seas during certain seasons. Pre-existing low pressure, large sea surface with a temperature higher than 27° C, and the presence of the Coriolis force are a must for tropical cyclone formation.
- At these locations, the local convectional currents acquire a whirling motion because of the Coriolis force generated by the earth’s rotation. After developing, these cyclones advance till they find a weak spot in the trade wind belt.
- Tropical cyclones always originate in large water bodies.
3.2.Temperate Cyclone
Temperate cyclones (Mid-Latitude cyclones), also known as Extratropical cyclones, are active over the mid-latitudinal regions between 35° latitude and 65° latitude in both hemispheres.
- They have a dynamic origin and cyclone formation is due to frontogenesis (interaction of cold and warm fronts). When the warm-humid air masses from the tropics meet the dry-cold air masses from the poles and thus a polar front is formed as a surface of discontinuity. The cold air pushes the warm air upwards from underneath. Thus, a void is created because of the lessening of pressure. The surrounding air rushed in to occupy this void and coupled with the earth’s rotation, a temperate cyclone is formed.
- Temperate cyclones can originate on both landmass or water.
4.How do cyclones form?
- A tropical cyclone originates in a region of low pressure, typically accompanied by clusters of thunderstorms. For this disturbance to evolve into a full-fledged cyclone, certain atmospheric and oceanic factors must align.
- The most crucial among these is a sufficiently warm sea surface — generally above 26.5°C — extending to a depth of around 50 metres. Moist air over such warm waters rises, cools, and condenses to form clouds, releasing latent heat in the process.
- This released heat warms the surrounding air, causing it to rise further and pull in more moist air from below, creating a self-sustaining cycle of convection.
- Another vital requirement is an unstable atmosphere, meaning that once air begins to rise, it continues to ascend instead of being forced downward. Additionally, the Coriolis effect — caused by Earth’s rotation — must be strong enough to induce a spinning motion.
- Because this effect is minimal near the equator, cyclones seldom form within about five degrees of latitude on either side of it.
- Low vertical wind shear is also necessary; if wind speed and direction differ greatly between the lower and upper atmosphere, the cyclone’s circulation can become disorganized and lose strength.
- As the system intensifies, a clearly defined centre known as the eye may develop. This calm, cloud-free zone is encircled by the eyewall — a ring of towering thunderstorms producing the strongest winds and heaviest rainfall.
- Near the surface, air spirals inward toward the low-pressure centre and ascends sharply at the eyewall, while at higher altitudes it spreads outward, completing the cyclone’s circulation pattern
5. How are cyclones named?
Cyclones that form in every ocean basin across the world are named by the regional specialised meteorological centres (RSMCs) and Tropical Cyclone Warning Centres (TCWCs). There are six RSMCs in the world, including the India Meteorological Department (IMD), and five TCWCs.
As an RSMC, the IMD names the cyclones developing over the north Indian Ocean, including the Bay of Bengal and the Arabian Sea, after following a standard procedure. The IMD is also mandated to issue advisories to 12 other countries in the region on the development of cyclones and storms.
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For Prelims: Indian and World Geography-Physical, Social, Economic Geography of India and the World For Mains: General Studies I: Important Geophysical phenomena such as earthquakes, Tsunami, Volcanic activity, cyclone etc., geographical features and their location-changes in critical geographical features and in flora and fauna and the effects of such changes |
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Previous Year Questions
1.Consider the following statements: (UPSC CSE 2020)
1. Jet streams occur in the Northern Hemisphere only.
2. Only some cyclones develop an eye.
3. The temperature inside the eye of a cyclone is nearly 10°C lesser than that of the surroundings.
Which of the statements given above is/are correct?
A. 1 Only
B. 2 and 3 Only
C. 2 Only
D. 1 and 3 Only
Answer (C)
2.In the South Atlantic and South-Eastern Pacific regions in tropical latitudes, cyclones do not originate. What is the reason? (UPSC Prelims GS1, 2015)
(a) Sea surface temperatures are low (b) Inter-tropical Convergence Zone seldom occurs (c) Coriolis force is too weak (d) Absence of land in those regions Answer (a)
1.Tropical cyclones are largely confined to South China Sea, Bay of Bengal and Gulf of Mexico. Why? (GS-1, 2014)
2.The recent cyclone on the east coast of India was called “Phailin”. How are the tropical cyclones named across the world? (GS-1, 2013) |
Source: indianexpress
