UPSC Prelims 2001 Q27: Geography – Atmosphere & Climatology
- (a) Both A and R are individually true, and R is the correct explanation of A
- (b) Both A and R are individually true, but R is NOT a correct explanation of A
- (c) A is true, but R is false
- (d) A is false, but R is true
Answer: (c) A is true, but R is false
Explanation
Assertion-Reason: anticyclonic conditions in the winter season
| Statement | Verdict |
|---|---|
| A. Anticyclonic conditions form in winter when atmospheric pressure is high and air temperatures are low | True — cold, sinking air over north-west India builds a high-pressure cell in winter |
| R. Winter rainfall in Northern India causes development of anticyclonic conditions | False — winter rainfall comes from western disturbances, which are low-pressure systems |
| Cause of the winter high | Subsidence under the subtropical westerly jet and radiative cooling of the land |
| Weather it brings | Clear skies, light winds, cold nights and fog |
In winter a high-pressure area lies over north-west India because the air is cold and sinking, which is what A says. Winter rain in Northern India is brought by western disturbances, which are depressions moving in from the Mediterranean, so rain does not cause the anticyclone. A is true and R is false. (Some third-party keys give (a); the facts support (c).)
Answer: (c) A is true, but R is false.
Why each option is right or wrong
- (a) Incorrect. R is false; western disturbances bring rain as low-pressure systems.
- (b) Incorrect. R is not true at all, so this cannot be the answer.
- (c) CORRECT. Winter anticyclones are real, but rainfall does not cause them.
- (d) Incorrect. A is true; high pressure and low temperature mark the winter season.
Key point
Western disturbances: extra-tropical lows carried by the westerly jet; give winter rain to Punjab and Haryana (good for rabi wheat) and snow to the Himalaya.
Remember
Winter high over north-west India; western disturbances (lows) bring the rain.
Common mistakes
- Thinking rain makes air colder and so creates the high-pressure cell.
- Forgetting that western disturbances are low-pressure systems.
- Marking (a) because both statements sound related.
Exam tip
Rain goes with low pressure; clear dry weather goes with high pressure.
Sources
- NCERT Class XI — India: Physical Environment, chapter 'Climate' (the cold weather season)
- India Meteorological Department — Western Disturbances (FAQ on winter weather)