Indian Geography — Cyclones
1. Introduction to Cyclones
Context: Tropical cyclones are regions of intense low-pressure that form over warm ocean waters. In India, they originate in the Bay of Bengal and the Arabian Sea.
- Definition: Regions of intense low-pressure with organized thunderstorms and cyclonic circulation.
- Latitudinal Range: 30° N and 30° S latitudes.
- Horizontal Extent: Up to 500-1,000 km.
- Vertical Extent: From surface to 12-14 km.
- Expansion of Wind Belt: 10-150 km.
📝 UPSC Previous Year Questions:
- UPSC Prelims 2019: In which months do tropical cyclones mostly form in the Bay of Bengal? Answer: October and November.
- UPSC Prelims 2017: What is the latitudinal range of tropical cyclones? Answer: 30°N and 30°S.
2. Distribution of Tropical Cyclones
Context: Tropical cyclones in India originate in the Bay of Bengal in the east and the Arabian Sea in the west.
- Origin Regions in India:
- Bay of Bengal — East coast
- Arabian Sea — West coast
- Season: Mostly Monsoon Season.
- Bay of Bengal Region: Months of October and November.
- Latitude: Between 10°-15° North latitudes.
📝 UPSC Key Points:
- Bay of Bengal: More cyclone-prone than Arabian Sea
- Peak Season: October-November (post-monsoon)
- Latitudinal Zone: 10°-15° North
3. Conditions for Tropical Cyclone Formation
- 1. Large and continuous supply of warm and moist air: Warm ocean waters (temperature >26°C) provide energy.
- 2. Strong Coriolis Force: Essential for cyclonic rotation; maximum at higher latitudes.
- 3. Unstable condition through the troposphere: Allows rising air and thunderstorm development.
- 4. Absence of strong vertical wind wedge: Low wind shear allows the cyclone to organize.
📝 UPSC Key Points:
- Warm Ocean: Temperature >26°C
- Coriolis Force: Essential for rotation
- Wind Shear: Low wind shear is favorable
- Moist Air: Continuous supply of warm and moist air
4. Characteristics of Tropical Cyclones
- Latitudinal Range: 30° N and 30° S latitudes.
- Horizontal Extent: Up to 500-1,000 km.
- Vertical Extent: From surface to 12-14 km.
- Expansion of Wind Belt: 10-150 km.
📝 UPSC Key Points:
- Latitude: 30°N - 30°S
- Size: 500-1,000 km horizontally
- Height: 12-14 km vertically
- Wind Belt: 10-150 km
5. Summary: Cyclones at a Glance
| Category | Details |
|---|---|
| Definition | Regions of intense low-pressure |
| Latitudinal Range | 30°N - 30°S |
| Horizontal Extent | 500-1,000 km |
| Vertical Extent | 12-14 km |
| Wind Belt Expansion | 10-150 km |
| Origin in India | Bay of Bengal & Arabian Sea |
| Peak Season (Bay of Bengal) | October-November |
| Latitude for Formation | 10°-15° North |
Key Takeaways for UPSC
- Tropical Cyclones: Regions of intense low-pressure; form between 30°N - 30°S
- Size: 500-1,000 km horizontally; 12-14 km vertically
- Origin in India: Bay of Bengal (more active) and Arabian Sea
- Peak Season: October-November (post-monsoon)
- Formation Latitude: 10°-15° North
- Conditions: Warm ocean (>26°C), strong Coriolis force, unstable atmosphere, low wind shear
High-Yield Interactive UPSC Quiz (Cyclones)
Q1. Tropical cyclones in India originate in which water bodies?
Correct Answer: B. Tropical cyclones in India originate in the Bay of Bengal in the east and the Arabian Sea in the west. The Bay of Bengal is more cyclone-prone.
Q2. In which months do tropical cyclones mostly form in the Bay of Bengal region?
Correct Answer: C. Tropical cyclones in the Bay of Bengal region mostly form during the months of October and November, the post-monsoon season. (UPSC 2019)
Q3. What is the latitudinal range of tropical cyclones?
Correct Answer: C. Tropical cyclones form between 30°N and 30°S latitudes. They do not form near the equator due to the lack of Coriolis force. (UPSC 2017)
Q4. Which of the following is NOT a condition for tropical cyclone formation?
Correct Answer: D. The absence of strong vertical wind wedge (low wind shear) is required for tropical cyclone formation. Strong vertical wind wedge disrupts cyclone organization.
Q5. The horizontal extent of a tropical cyclone can be up to:
Correct Answer: C. The horizontal extent of a tropical cyclone can be up to 500-1,000 km, while the vertical extent is from the surface to 12-14 km.
Q6. What is the vertical extent of a tropical cyclone?
Correct Answer: C. The vertical extent of a tropical cyclone is from the surface to 12-14 km, reaching the tropopause.
Q7. The expansion of the wind belt in a tropical cyclone ranges from:
Correct Answer: C. The expansion of the wind belt in a tropical cyclone ranges from 10 to 150 km, with the strongest winds near the eyewall.
Q8. Which of the following is essential for the formation of a tropical cyclone?
Correct Answer: C. Strong Coriolis Force is essential for cyclonic rotation. Without it, tropical cyclones cannot form, which is why they don't form near the equator.
Q9. What is the preferred latitudinal zone for tropical cyclone formation?
Correct Answer: C. Tropical cyclones form between 10°-15° North latitudes, where the Coriolis force is strong enough and ocean waters are warm (>26°C).
Q10. The Bay of Bengal region experiences tropical cyclones mostly during:
Correct Answer: B. The Bay of Bengal region experiences tropical cyclones mostly during the post-monsoon season (October-November), though some also occur during the pre-monsoon season (April-May). (UPSC 2019)