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💡 The valley breathes
By day, sun-warmed slopes send air rising and pull a breeze up from the valley; by night it reverses. Hill towns like Shimla feel this daily rhythm.
What are valley and mountain breezes?
How do valley and mountain breezes differ?
Local breezes
Day or night?
1. Valley breeze
Blows during the day
Example:
Air rises up the slope
2. Mountain breeze
Blows after sunset
Example:
Air sinks to the valley
- By day , sun-facing slopes heat faster than the valley floor; warm air rises and cooler valley air flows up the slopes — a valley breeze (Fig. 13.8a).
- After sunset the slopes cool faster; the cooler, denser air flows down into the valley — a mountain breeze (Fig. 13.8b).
- These daily wind changes are felt in hilly regions like Shimla and Dehradun and help regulate temperature, moisture and crop health.
NCERT Question 5 — How are mountain and valley
How are mountain and valley breezes formed? Suppose there are two mountains, one covered with grass and another covered with barren rocks; would the temperature of the two mountain breezes be different? If so, how?
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Valley Breeze vs Mountain Breeze
Valley breeze
Mountain breeze
Blows during the day
Blows after sunset (night)
Slopes heat faster; warm air rises
Slopes cool faster; cool air sinks
Air flows up from the valley to the slopes
Air flows down the slopes into the valley
Important Definitions
- Local winds — winds produced by the uneven heating of the Earth’s surface over a small area, such as valley and mountain breezes.
- Valley breeze — the daytime upslope flow of cooler valley air that replaces the warm air rising from sun-heated mountain slopes.
- Mountain breeze — the night-time downslope flow of cool, dense air from the mountain slopes into the warmer valley.
