UPSC Prelims 2020 Q99: Geography – Atmosphere & Climatology
Consider the following statements:
1. Jet streams occur in the Northern Hemisphere only.
2. Only some cyclones develop an eye.
3. The temperature inside the eye of a cyclone is nearly 10°C lesser than that of the surroundings.
Which of the statements given above is/are correct?
- (a) 1 only
- (b) 2 and 3 only
- (c) 2 only
- (d) 1 and 3 only
Answer: (c) 2 only
Explanation
Jet Streams & Cyclones: Atmospheric Phenomena
| Statement | Claim | Verdict | Detail |
|---|---|---|---|
| 1 | Jet streams occur in Northern Hemisphere only | FALSE | Jet streams occur in BOTH hemispheres (polar jet, subtropical jet). Southern Hemisphere as strong as Northern. |
| 2 | Only some cyclones develop eye | TRUE | Eye forms in intense cyclones (Category 3+). Weak cyclones lack eyes. Eye = organized vortex center. |
| 3 | Eye temperature ~10°C LESS than surroundings | FALSE | Eye is WARMER than surroundings (subsidence heating, adiabatic). Temperature IN eye > outside. |
Only statement 2 is correct. Answer: (c) 2 only.
Answer: (c) 2 only.
Why each option is right or wrong
- (a) Incorrect. Statement 1 is false (jet streams in both hemispheres).
- (b) Incorrect. Statement 3 is false (eye is warmer, not cooler).
- (c) CORRECT. Only statement 2 (some cyclones have eyes) is true. Statements 1 and 3 are factually wrong.
- (d) Incorrect. Statement 3 is false.
Key point
Jet streams: Both hemispheres. Polar jet (~60° latitude), Subtropical jet (~30° latitude). Stronger in winter, drive surface weather patterns globally.
Remember
Jet streams occur in BOTH hemispheres, not only Northern (Statement 1 false). Only SOME cyclones (intense ones) develop eyes (Statement 2 true). The eye is WARMER than surroundings due to subsidence heating, not cooler (Statement 3 false). Answer: 2 only.
Common mistakes
- Confusing polar jet (Northern weak, Southern strong) average. Actually both active, seasonal variation.
- Inverting eye temperature - subsidence (sinking air) in eye warms it adiabatically -> warmer than surrounding air (cooler from evaporative cooling at eyewall).
- Assuming all cyclones have eyes. Weak tropical storms, subtropical cyclones often lack organized eyes.
Exam tip
Eye dynamics: Eyewall = coldest (evaporative cooling, updrafts). Eye = warmer (subsidence heating). Ring of maximum wind = eyewall.
Sources
- NOAA - Jet Stream and Hurricane Formation
- WMO - Atmospheric Circulation Patterns