What is a Cyclone?
Cyclones are powerful, fast-moving winds that spiral towards a low-pressure area. You can think of them as nature’s giant spinning storm systems that pull air inward, causing heavy rain, strong winds, and sometimes flooding.
The word “cyclone” comes from the Greek word “cyclos”, which means “coils of a snake” — because the winds move in a spiral, just like a coiled snake.
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In the Northern Hemisphere, the winds spin anticlockwise.
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In the Southern Hemisphere, they spin clockwise.
This spinning happens because of the Coriolis effect, caused by Earth's rotation.
Types of Cyclones
1. Tropical Cyclones
These form over warm oceans near the equator and are very intense. Examples include Cyclone Fani, Amphan, and Biparjoy. We'll explore these in detail below.
2. Temperate (or Extra-Tropical) Cyclones
These form in mid-latitude regions (like Europe, North America), usually during winter, and are larger but less intense than tropical cyclones.
Temperate Cyclones (Also Called Extra-Tropical Cyclones)
Temperate cyclones are large weather systems that affect areas in the middle latitudes — that means regions between the tropics and the polar areas. They are also called extra-tropical cyclones because they form beyond the Tropic of Cancer and Tropic of Capricorn.
You’ll often hear about them in news from Europe, North America, or Central Asia — they bring rain, snow, and strong winds, especially during winters.
Key Features of Temperate Cyclones
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Where They Form:
Temperate cyclones form between 35° to 65° latitude in both the Northern and Southern Hemispheres.
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How They Form:
These cyclones are created when two different air masses — one warm and one cold — meet. This leads to the formation of a front, which triggers cyclonic activity.
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Shape:
Their shape can vary — some are circular, some semi-circular, while others may look elliptical or stretched.
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Size/Spread:
They are quite large — usually spread over 500 to 600 kilometers.
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Wind Speed:
The wind speed in temperate cyclones is moderate, around 30 to 40 km/h, but the overall system can travel fast and affect wide areas.
Formation of Temperate Cyclone (Polar Front Theory)
The formation of temperate cyclones is best explained by the Polar Front Theory, given by Bjerknes and Bjerknes. It involves six key stages:
1. Initial Stage
Two air masses — one warm and one cold — move parallel to each other, creating a stationary front.
2. Incipient Stage
The air masses start to interact, forming a wave-like front as each mass pushes into the other.
3. Mature Stage
A full cyclone develops. The isobars (pressure lines) become nearly circular, and the system intensifies.
4. Narrowing of Warm Sector
The cold front, being faster, starts pushing into the warm sector, squeezing it and making it narrower.
5. Occlusion Stage
The cold front overtakes the warm front, forming an occluded front — where both fronts merge.
6. Dissipation Stage
The warm air is lifted completely, the energy weakens, and the cyclone dies out.
Distribution of Temperate Cyclones (Extra-Tropical Cyclones)
Temperate cyclones don’t form randomly. They usually appear in regions where cold and warm air masses meet sharply. Here's where they are most commonly found:
1. Atlantic–Arctic Front (North Atlantic Ocean)
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The North Atlantic Ocean is relatively warm, while the Arctic air is extremely cold.
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When these two air masses collide, a strong temperature contrast is created.
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This leads to low-pressure development and the cyclone moves northeast, often affecting Western Europe.
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These are the famous cyclones that bring stormy winters to Europe.
2. North America Polar Front (Great Lakes Region)
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Cold Polar air meets warmer air over North America, especially around the Great Lakes.
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This contrast leads to cyclone formation that moves northeastward, impacting Canada and the northeastern US.
3. Mediterranean–Caspian Front
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Cold continental air from northern landmasses meets warmer air from the Mediterranean and Caspian Seas.
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This zone becomes a breeding ground for temperate cyclones.
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These cyclones often travel eastward and cause Western Disturbances — responsible for winter rain in northwestern India.
4. Southern Hemisphere (35°–65° S Latitude)
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The Southern Hemisphere has fewer landmasses, so temperature contrasts are less intense.
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Still, temperate cyclones do form between 35° and 65° South, mainly over oceans.
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They generally move southeastward but are less intense compared to the Northern Hemisphere.
Tropical Cyclones
Tropical cyclones are intense, violent storms that form over warm ocean waters in tropical regions. These storms are known for causing widespread destruction, especially along coastal areas lying between the Tropic of Cancer and Tropic of Capricorn.
They can bring extremely heavy rainfall, very strong winds, storm surges, and even flooding, making them one of the most dangerous natural disasters.
Key Features of Tropical Cyclones
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Location:
These storms form within the tropical zone, i.e., between the Tropic of Cancer (23.5°N) and Tropic of Capricorn (23.5°S).
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Spread & Size:
Tropical cyclones are smaller in size than temperate cyclones. Their diameter ranges from 30 km to 300 km, though some may grow larger.
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Origin:
They are of thermal origin, meaning they form due to heat and moisture. Warm ocean water fuels the storm by releasing latent heat of condensation, which powers the cyclone like a self-sustaining heat engine.
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Shape:
Tropical cyclones have a spiral (circular) shape, with a calm center called the eye surrounded by intense storm clouds.
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Wind Speed:
Their speed can vary from 32 km/h to over 180 km/h — sometimes even more in super cyclones.
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Direction of Wind Rotation:
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In the Northern Hemisphere, the winds rotate counter-clockwise.
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In the Southern Hemisphere, they rotate clockwise.
This is due to the Coriolis Effect, which is caused by Earth's rotation.
Conditions Needed for Tropical Cyclone Formation
Tropical cyclones need a special set of conditions to form. Here are the key ones:
1. Warm Ocean Waters
2. Plenty of Moisture
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Evaporation from the ocean supplies moisture.
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Moist air rises, condenses, and releases latent heat, which powers the storm.
3. Coriolis Force
4. Pre-existing Low Pressure
5. Favourable Upper-Air Conditions
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Light winds above allow the cyclone to grow.
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Strong wind shear can weaken or destroy it.
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An anti-cyclone above helps intensify the system.
Distribution of Tropical Cyclones (Where They Form)
Tropical cyclones form over warm oceans between the Tropic of Cancer and Tropic of Capricorn. Here’s where they commonly occur:
1. North Atlantic Ocean
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Areas: Caribbean Sea, Gulf of Mexico, and U.S. east coast
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Peak Season: August to October
2. Indian Ocean
3. South Indian Ocean
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Areas: Madagascar, Reunion Islands, Timor Sea (NW Australia)
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Peak Season: January to March
4. North Pacific Ocean (Eastern)
5. North Pacific Ocean (Western)
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World’s most active region
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Areas: Philippines, South China Sea, Japan region
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Peak Season: August to September
6. South Pacific Ocean (Western)
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Areas: East coast of Australia, Fiji, Samoa, Coral Sea
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Peak Season: January to March
Structure of a Tropical Cyclone
A tropical cyclone has a well-defined structure made up of three main parts:
1. The Eye
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The eye is the calm center of the cyclone.
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Winds rotate around it.
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It has low pressure, clear skies, and descending air.
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Diameter can range from 8 km to 200 km.
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Smaller eye = stronger cyclone.
2. The Eyewall
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This is a ring of dense clouds and strong winds surrounding the eye.
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It is the most violent part of the cyclone, with heavy rain and powerful updrafts.
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Maximum destruction usually happens here.
3. Rain Bands
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These are spiral-shaped bands of clouds and rain extending out from the eyewall.
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They bring rainfall even far from the center of the storm.
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Made up of cumulonimbus clouds, they move with the storm.
Formation of Tropical Cyclone
Tropical cyclones usually form over warm tropical oceans, especially during late summer (August to November). Their formation happens in three main stages:
1. Early Stage
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Warm ocean water (above 27°C) heats the air above it.
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This warm, moist air rises, cools, and condenses into clouds, releasing latent heat (energy).
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This heat makes the air rise even more, forming a strong updraft.
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Due to the Coriolis effect, the rising air begins to spin, creating a spiral or vortex.
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As more air rushes in, the storm grows and intensifies.
2. Mature Stage
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A well-developed eye forms at the center — calm and clear.
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Surrounding the eye is the eyewall, where the strongest winds and rainfall occur.
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Rain bands (made of thick cumulonimbus clouds) spiral outward from the center.
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The cyclone now behaves like a self-sustaining heat engine, powered by the release of latent heat.
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It moves along with the trade winds, gaining more energy from the warm ocean.
3. Decaying Stage
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When the cyclone moves over land or cold water, it loses its fuel — moisture and heat.
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Also, friction with land weakens the wind.
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The cyclone gradually loses strength and dies out.
Tropical Cyclones and Their Naming
Tropical cyclones are given names to make communication easier and to avoid confusion, especially when multiple storms happen at the same time.
Each year, names are used in a fixed alphabetical order, based on a list created by the World Meteorological Organization (WMO) for different regions.
Who Names the Cyclones?
In the Indian Ocean region, the names are suggested by 8 countries:
India, Bangladesh, Maldives, Myanmar, Oman, Pakistan, Sri Lanka, and Thailand
Each country submits a list of names, and whenever a cyclone forms, the next name on the list is used.
Why Naming is Important?
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Helps in quick identification of storms.
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Avoids confusion when more than one cyclone is active in a region.
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Makes it easier for the media and public to track and remember
Anticyclones – The Calm High-Pressure Systems
An anticyclone is a large, high-pressure weather system found in mid-latitudes. It’s usually bigger than a cyclone and moves west to east along with the westerly winds.
Unlike cyclones, anticyclones bring clear skies and calm weather.
Key Features of Anticyclones
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High Pressure Zone:
Air descends from above and then diverges outward near the surface.
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Wind Direction:
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No Fronts or Conflicting Air Masses:
Since there's no clash of air masses, no fronts are formed.
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Weather Conditions:
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Wind Speed:
Winds are very light at the center and increase outward.
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Stagnation:
Sometimes, anticyclones stay in one place for days, causing air pollution to build up.
Cyclones vs Anticyclones – Key Differences
| Feature | Cyclones | Anticyclones |
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| Pressure | Low pressure at the center, surrounded by high pressure | High pressure at the center, surrounded by low pressure |
| Wind Movement | Winds blow towards the center | Winds blow outward from the center |
| Wind Intensity | Strong and destructive winds | Mild and gentle winds |
| Rotation (Northern Hemisphere) | Anticlockwise | Clockwise |
| Rotation (Southern Hemisphere) | Clockwise | Anticlockwise |
| Weather | Cloudy skies, thunderstorms, heavy rain | Clear skies, dry and calm weather |
| Impact | Often causes floods, storms, and damage | Usually associated with stable, pollution-prone air
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Conclusion
Cyclones and anticyclones are powerful weather systems that shape the climate and impact life across the globe. While cyclones bring violent storms, rain, and destruction, anticyclones bring calm, clear, and dry weather.
Understanding their formation, structure, behavior, and differences is not only important for UPSC and other exams, but also helps us become more aware of the forces of nature around us.
With climate change increasing the intensity and frequency of tropical cyclones, knowing how these systems work is more relevant than.
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