The correct option is Valley breeze.
Explanation
Local winds are small-scale circulations generated by local thermal differences. In mountainous terrain, the diurnal cycle of heating and cooling creates a periodic wind system known as mountain and valley breezes.Mechanism of Valley Breeze:
- Daytime Heating: During the day, the mountain slopes are heated by the sun more intensely than the air at the same altitude over the valley floor.
- Pressure Gradient: The air in contact with the warm slopes expands, becomes less dense, and rises, creating a zone of low pressure along the slopes.
- Air Movement: To fill the void left by the rising air, cooler air from the valley moves up the slopes. This upslope wind is known as the Valley Breeze (or Anabatic wind).
Analysis of Incorrect Options:
- Mountain wind Mountain wind: This occurs at night. As the slopes cool rapidly through terrestrial radiation, the air becomes cold and dense, draining down into the valley (Katabatic wind).
- Land breeze & Sea breeze Land and Sea breezes: These are local winds found in coastal regions caused by the differential heating of land and water bodies, not specific to mountainous terrain.
Key Takeaway:
Valley Breezes blow upslope during the day due to thermal instability, whereas Mountain Winds blow downslope at night due to gravitational drainage of cold air.