UPSC Prelims 2011 Q89: Geography – Atmosphere & Climatology
Westerlies in southern hemisphere are stronger and persistent than in northern
hemisphere. Why?
1. Southern hemisphere has less landmass as compared to northern hemisphere.
2. Coriolis force is higher in southern hemisphere as compared to northern hemisphere
Which of the statements given above is/are correct?
- (a) 1 only
- (b) 2 only
- (c) Both 1 and 2
- (d) Neither 1 nor 2
Answer: (a) 1 only
Explanation
Why Southern Hemisphere Westerlies are stronger
The Westerlies are prevailing winds in the mid-latitudes, and their strength differs by hemisphere.
| Statement | Verdict | Reason |
|---|---|---|
| 1. Southern Hemisphere has less landmass than Northern Hemisphere | Correct | With less landmass to create friction, the Southern Hemisphere's winds blow more unobstructed and strongly over vast ocean expanses |
| 2. Coriolis force is higher in the Southern Hemisphere | Incorrect | The Coriolis force depends on latitude and Earth's rotation, and is essentially the same at equivalent latitudes in both hemispheres — it is not inherently 'higher' in the south |
Why Southern Westerlies are stronger:
| Point | Detail |
|---|---|
| Key factor | Less landmass → less frictional drag |
| Coriolis force | Same magnitude at equivalent latitudes in both hemispheres |
| Result | Persistent, strong Westerlies, sometimes called the 'Roaring Forties' |
Answer: (a) 1 only.
Why each option is right or wrong
- (a) CORRECT. Less landmass in the Southern Hemisphere means less frictional obstruction, letting Westerlies blow stronger and more persistently.
- (b) Incorrect. The Coriolis force is not inherently higher in the Southern Hemisphere; it depends on latitude, which is symmetric between hemispheres.
- (c) Incorrect. Statement 2's Coriolis claim is false, so 'both' cannot be correct.
- (d) Incorrect. Statement 1 is accurate, so 'neither' is wrong.
Key point
Southern Hemisphere Westerlies are stronger mainly because of LESS LANDMASS (less friction) — NOT because the Coriolis force is somehow 'higher' there; Coriolis force depends on latitude, symmetric in both hemispheres.
Remember
Southern Hemisphere's stronger Westerlies: due to less landmass/friction, NOT a hemisphere-specific difference in Coriolis force.
Common mistakes
- Assuming the Coriolis force differs fundamentally between hemispheres at the same latitude.
- Missing the landmass-friction explanation as the real driver of wind strength differences.
- Overcomplicating a simple geography-based (ocean vs land) explanation with incorrect physics.
Exam tip
Southern Hemisphere = more ocean, less land, less friction = stronger Westerlies. Coriolis force itself is latitude-symmetric, not hemisphere-biased.
Sources
- NCERT Class XI Geography — Fundamentals of Physical Geography — Atmospheric Circulation and Weather Systems
- Savindra Singh — Climatology (Prayag Pustak Bhawan)