The correct option is 2 only.
Explanation
Mountain and valley winds are local diurnal wind systems driven by the differential heating and cooling of mountain slopes and valley floors. These thermal differences create pressure gradients that reverse airflow direction between day and night.
Statement-wise Analysis
- Statement 1 is Incorrect. During the day, the mountain slopes heat up more rapidly than the valley floor. The air above the slopes becomes warmer, expands, and rises. Consequently, air from the valley flows up the slope to replace the rising air. This upslope wind is known as the valley breeze (or anabatic wind), not the mountain breeze.
- Statement 2 is Correct. During the night, the mountain slopes cool down rapidly due to terrestrial radiation. The air in contact with the cold slopes becomes dense and heavy. Under the influence of gravity, this cool air descends into the valley. This downslope wind is known as the mountain breeze.
- Statement 3 is Incorrect. Katabatic wind refers to the downslope flow of cold, dense air (mountain breeze) occurring at night or over ice caps. The warm air rising from the valley floor up the slopes is technically termed an anabatic wind.
Key Takeaway
Valley Breeze (Anabatic): Occurs during the day; warm air moves upslope.
Mountain Breeze (Katabatic): Occurs during the night; cold air moves downslope due to gravity.