UPSC Prelims 2024 Q14: Geography – Atmosphere & Climatology
With reference to “Coriolis force”, which of the following statements is/are correct ?
1. It increases with increase in wind velocity.
2. It is maximum at the poles and is absent at the equator.
Select the answer using the code given below :
- (a) 1 only
- (b) 2 only
- (c) Both 1 and 2
- (d) Neither 1 nor 2
Answer: (c) Both 1 and 2
Explanation
Coriolis Force — Properties
| Statement | Claim | Verdict | Why |
|---|---|---|---|
| 1 | Coriolis force increases with wind velocity | TRUE | Coriolis force formula: F = 2mΩv sinφ where Ω = Earth's angular velocity, v = wind speed, φ = latitude. Force is directly proportional to velocity (v) - faster winds experience greater Coriolis deflection. |
| 2 | Coriolis force is maximum at poles, absent at equator | TRUE | From formula: sinφ factor. At poles (φ = 90°): sin 90° = 1 (maximum). At equator (φ = 0°): sin 0° = 0 (absent/zero). This is why cyclones cannot form at the equator (no Coriolis force to initiate spin). |
Coriolis Force Key Properties:
| Property | Detail |
|---|---|
| Direction | Right in Northern Hemisphere, Left in Southern Hemisphere |
| Causes | Deflection of winds, ocean currents, projectiles |
| Max latitude | Poles (sin 90° = 1) |
| Min latitude | Equator (sin 0° = 0) - hence no cyclones at equator |
| Proportional to | Wind velocity AND latitude |
| NOT a real force | It is an apparent force - result of Earth's rotation |
Both statements 1 and 2 are correct.
Answer: (c) Both 1 and 2.
Why each option is right or wrong
- (a) Incorrect. 'Only 1' would make statement 2 wrong — but Coriolis force is demonstrably zero at the equator (sin 0° = 0) and maximum at poles (sin 90° = 1). This is why cyclones cannot cross the equator.
- (b) Incorrect. 'Only 2' would make statement 1 wrong — the Coriolis force formula explicitly includes wind velocity (v). Higher velocity winds are deflected more by Coriolis force.
- (c) CORRECT. Both are true. Coriolis force increases with wind velocity (F ∝ v) AND is maximum at poles (sin 90°) and absent at equator (sin 0°).
- (d) Incorrect. 'Neither' would contradict the mathematical formula for Coriolis force (2mΩv sinφ), which is a fundamental equation in atmospheric dynamics.
Key point
Coriolis force = 2mΩv sinφ. Increases with velocity (∝ v). Maximum at poles (sin 90° = 1). Zero at equator (sin 0° = 0). NH = deflects right. SH = deflects left. No cyclones at equator.
Remember
Coriolis force increases with wind velocity and is maximum at poles (sin 90°) but absent at the equator (sin 0°). This is why cyclones cannot form or cross the equator.
Common mistakes
- Thinking Coriolis force is constant regardless of latitude — it varies with sin(latitude), being zero at equator and maximum at poles.
- Not knowing Coriolis force increases with wind speed — faster winds are deflected more, which affects upper-level jet streams more than surface winds.
- Forgetting that the absence of Coriolis force at the equator explains why tropical cyclones cannot form within 5° of the equator.
Exam tip
Coriolis force mnemonic: 'VLAT' = Velocity increases it, Latitude determines it (sin φ), Absent at equator, Twin maxima at poles. Formula: F = 2mΩv sinφ. NH = right deflection. SH = left deflection.
Sources
- NCERT Class 11 Geography — Chapter 10: Atmospheric Circulation and Weather Systems
- IMD — Coriolis Effect and Tropical Cyclones