What is the Föhn wind effect?

The Föhn wind effect refers specifically to the phenomenon where moist air rises over a mountain range, cools as it rises, and then warms again as it descends on the leeward side. This warming occurs because, as air descends, it is compressed, which causes it to heat up. The Föhn wind is characterized by dry and warm air that can lead to a sudden increase in temperature and can have significant impacts on local weather conditions.

In this context, option B correctly captures the essence of the Föhn wind effect by describing the warming of air that rises over high terrain. The effect often leads to clearer skies and warmer temperatures on the leeward side of the mountains, making it a notable climatic phenomenon in regions where it occurs.

The other options, while they may pertain to meteorological concepts, do not accurately depict the Föhn wind effect. Specifically, the cooling of air during its descent is not the correct focus, as the defining feature is the warming upon descent after expansion. Similarly, simple changes in air pressure due to temperature variations and wind shear do not encapsulate the specific characteristics associated with the Föhn wind.