What is the primary cause of valley breezes?

What is the primary cause of valley breezes?

• A. Terrain roughness
• B. Solar heating of valley slopes
• C. Jet stream influence
• D. Moisture gradient

Answer: (B)

Valley breezes are driven by daytime solar heating of valley slopes. When the sun warms the slopes, the air along those surfaces becomes buoyant and rises. To replace the rising air, cooler air from the valley floor moves upslope toward the bases of the slopes, creating a gentle, upslope breeze that starts in the valley and flows up the sides. This daytime, slope-heating circulation is strongest on sunny, calm days when solar heating dominates other influences. Other factors like terrain roughness can tweak winds locally, and jet streams are far above the valley or moisture differences are not the main driver, but they don’t cause the valley breeze the way slope heating does.

Valley breezes are driven by daytime solar heating of valley slopes. When the sun warms the slopes, the air along those surfaces becomes buoyant and rises. To replace the rising air, cooler air from the valley floor moves upslope toward the bases of the slopes, creating a gentle, upslope breeze that starts in the valley and flows up the sides. This daytime, slope-heating circulation is strongest on sunny, calm days when solar heating dominates other influences. Other factors like terrain roughness can tweak winds locally, and jet streams are far above the valley or moisture differences are not the main driver, but they don’t cause the valley breeze the way slope heating does.