CAPF AC 2022 Q6: Geography – Atmosphere & Climatology
Trough and ridge are
- (a) elongated area of low pressure and of high pressure respectively
- (b) elongated areas of low pressure
- (c) elongated areas of high pressure
- (d) elongated area of high pressure and of low pressure respectively
Answer: (a) elongated area of low pressure and of high pressure respectively
Explanation
Trough and ridge on a weather map
How to think: borrow the picture from land.
A trough is a long dip, so it is low.
A ridge is a long raised line, so it is high.
On a weather map the height is air pressure.
| Term | Pressure | Shape of isobars | Weather |
|---|---|---|---|
| Trough | Elongated low | Bend away from the low centre | Cloud and rain |
| Ridge | Elongated high | Bend away from the high centre | Clear and settled |
| Depression or cyclone | Closed low | Closed circles | Stormy |
| Anticyclone | Closed high | Closed circles | Fine |
Indian example: the monsoon trough is a long belt of low pressure across the northern plains in the rainy season.
Answer: (a).
Why each option is right or wrong
- (a) CORRECT. A trough is an elongated low and a ridge an elongated high.
- (b) Incorrect. Only the trough is a low; the ridge is a high.
- (c) Incorrect. Only the ridge is a high; the trough is a low.
- (d) Incorrect. This reverses the two terms.
Key point
Trough = elongated low pressure (rain). Ridge = elongated high pressure (fair weather). Monsoon trough and western disturbances are troughs that matter for India.
Remember
Trough = long low; ridge = long high.
Common mistakes
- Reversing the two and calling a ridge a low pressure area.
- Thinking both terms describe the same kind of pressure system.
- Confusing a trough with a closed low such as a depression or cyclone.
Exam tip
Educated guess: a trough is what animals drink from, a hollow. A ridge is the top line of a hill. Hollow is low, hilltop is high.
Sources
- NCERT Class XI Geography — Fundamentals of Physical Geography, Chapter 10: Atmospheric Circulation and Weather Systems
- India Meteorological Department — Glossary of meteorological terms (trough, ridge)