A valley breeze occurs when the sun heats the slopes of a valley more quickly than the valley floor or the surrounding atmosphere, causing warmer, less dense air to rise and create an upslope wind.
A valley breeze is primarily caused by the difference in heating between altitudes. During the day, the sun heats the slopes of a valley more quickly than the valley floor or the surrounding atmosphere. As a result, the air near the slopes becomes warmer and less dense, so it begins to rise, creating an upslope wind. This mechanism is different from other types of breezes, like sea breezes, which are caused by the difference in heating between the land and sea due to the varying specific heat capacities of water and land surfaces.
Heat transfer occurs due to temperature differences between systems, leading to air movement, and this is the core process behind valley breezes. The warming of air on the valley sides during the day causes the less dense, warmer air to rise, generating a breeze that flows from the valley towards higher elevations. At night, this process can reverse, creating a mountain breeze as the valley sides cool more rapidly than the air above, leading to denser, cooler air descending into the valley.