Cyclones: Tropical & Temperate
How tropical and temperate cyclones form and differ — the structure of a tropical cyclone, the conditions for its formation, and the naming across ocean basins.
Key Takeaways
- Tropical cyclones form over warm oceans (SST above ~26.5°C) and have a calm 'eye' surrounded by a violent eye wall.
- Temperate cyclones form along the polar front where warm and cold air masses meet.
- The same storm is called a hurricane, typhoon or cyclone depending on the ocean basin.
Core concept
A cyclone is a system of winds spiralling inward toward a low-pressure centre. Tropical cyclones are compact, intensely destructive storms of the warm oceans; temperate (extratropical) cyclones are larger, milder systems of the mid-latitudes formed where air masses collide.
Static foundation — conditions for a tropical cyclone
- A warm ocean (sea-surface temperature above ~26.5°C) to a good depth — the energy source.
- Coriolis force — so they form beyond ~5° latitude, never on the equator.
- Low vertical wind shear and a pre-existing disturbance with upper-air divergence.
Structure of a Tropical Cyclone
Tropical vs Temperate Cyclones
| Feature | Tropical Cyclone | Temperate Cyclone |
|---|---|---|
| Location | Warm tropical oceans (0°–30°) | Mid-latitudes (35°–65°), along the polar front |
| Energy source | Latent heat from warm ocean water | Temperature contrast between air masses (fronts) |
| Size & intensity | Small but very violent | Large but less violent |
| Fronts | No fronts | Formed along a warm and a cold front |
| Season | Late summer / autumn | Winter (brings rain to NW India as western disturbances) |
Cyclone Names Around the World
Tap to reveal the basin.
Why India's east coast is more cyclone-prone
The Bay of Bengal is warmer and calmer than the Arabian Sea, has higher humidity and freshwater inflow from rivers, and receives storm remnants from the Pacific — so the east coast (Odisha, Andhra, Tamil Nadu, West Bengal) faces far more cyclones than the west. The IMD names cyclones in the region from an agreed regional list.
Relevance & current linkage
Improved cyclone early-warning systems have sharply cut death tolls (e.g., since the 1999 Odisha super cyclone). Warming seas may raise cyclone intensity. (Add a recent named cyclone and its impact if relevant.)
Prelims trap zones
- The eye is the CALM, clear centre; the eye wall has the most violent winds.
- Tropical cyclones have no fronts; temperate cyclones form along fronts.
- Western disturbances (temperate cyclones from the Mediterranean) bring winter rain to NW India — vital for the rabi crop.
Knowledge Check
2 questions · check your understanding
1. The calm, cloud-free centre of a tropical cyclone is called the:
2. Winter rainfall in north-west India is mainly brought by:
Prelims Pointers
- Tropical cyclones do NOT form within about 5° of the equator (the Coriolis force is too weak).
- In the Indian Ocean they are called 'cyclones'; in the Atlantic 'hurricanes'; in the NW Pacific 'typhoons'.
- Temperate cyclones bring winter rain to north-west India as 'western disturbances'.
- The IMD classifies systems from a depression up to a super cyclonic storm by wind speed.
Mains Angle
- 'The eastern coast of India is more cyclone-prone than the west.' Explain.
- Compare the origin and characteristics of tropical and temperate cyclones.
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