What primarily causes Advection Fog to form?

Advection fog forms primarily when warm, moist air moves horizontally over a colder surface, such as cooler land or ocean waters. This movement causes the temperature of the air to decrease to its dew point, leading to condensation and the formation of fog. In this process, the moisture in the warm air cools as it comes into contact with the cooler surface, resulting in tiny water droplets that make up the fog.

The other options describe different meteorological phenomena. For instance, evaporation from warm water bodies can generate steam fog under certain conditions, but it does not relate to the horizontal movement of air that characterizes advection fog. A drop in atmospheric pressure can influence weather patterns but is not a direct cause of advection fog formation. Similarly, cold air sinking over warm land can lead to other forms of fog, such as radiation fog, but does not pertain to the mechanism of advection fog, which is specifically tied to the movement of warm air across cooler surfaces.