UPSC Prelims 2011 Q95: Geography – Atmosphere & Climatology
The jet aircrafts fly very easily and smoothly in the lower stratosphere. What could be the
appropriate explanation?
1. There are no clouds or water vapour in the lower stratosphere.
2. There are no vertical winds in the lower stratosphere.
Which of the statements given above is/are correct in this context?
- (a) 1 only
- (b) 2 only
- (c) Both 1 and 2
- (d) Neither 1 nor 2
Answer: (c) Both 1 and 2
Explanation
Why jets fly smoothly in the lower stratosphere
The lower stratosphere offers a particularly stable flying environment for jet aircraft.
| Statement | Verdict | Reason |
|---|---|---|
| 1. No clouds or water vapour in the lower stratosphere | Correct | The stratosphere is very dry, with minimal water vapour and generally no clouds, avoiding weather-related turbulence |
| 2. No vertical winds in the lower stratosphere | Correct | Unlike the turbulent, convective troposphere, the stratosphere is stable and stratified, largely lacking strong vertical air currents |
Why the stratosphere suits jet cruising:
| Point | Detail |
|---|---|
| Moisture | Very dry, essentially cloud-free |
| Air movement | Stable, stratified, minimal vertical currents |
| Result | Smooth, predictable flying conditions for jets |
Answer: (c) Both 1 and 2.
Why each option is right or wrong
- (a) Incorrect. Statement 2 (no vertical winds) is also correct, so '1 only' is incomplete.
- (b) Incorrect. Statement 1 (no clouds/water vapour) is also correct, so '2 only' is incomplete.
- (c) CORRECT. Both the absence of clouds/water vapour and the lack of vertical winds make the lower stratosphere ideal for smooth jet flight.
- (d) Incorrect. Since both statements are accurate, 'neither' is wrong.
Key point
Jets fly smoothly in the lower stratosphere because it is dry/cloud-free AND stable with no significant vertical winds — both factors together explain the smooth ride.
Remember
Lower stratosphere: dry/cloud-free AND stable with no vertical winds — both explain why jets fly smoothly there.
Common mistakes
- Assuming only one factor (dryness OR stability) explains the smooth flight, missing the other.
- Confusing the stratosphere's stability with the turbulent, convective troposphere below it.
- Not connecting lack of water vapour to the absence of storm-related turbulence.
Exam tip
Stratosphere = dry + stable (no vertical winds). Both properties combine to give jets their smooth high-altitude ride.
Sources
- NCERT Class XI Geography — Fundamentals of Physical Geography — Composition and Structure of Atmosphere
- Savindra Singh — Climatology (Prayag Pustak Bhawan)