What is advection fog?

Advection fog occurs when warm, moist air moves horizontally over a cooler surface, which causes condensation as the air cools. This process is primarily driven by the movement of air masses; when warm air flows over cooler land or water, it loses heat and its capacity to hold moisture decreases, leading to the formation of fog. Commonly, this type of fog can be observed near coastal areas where warm air from the sea interacts with colder air or surfaces.

The other options describe different types of fog or conditions but do not specifically involve the horizontal movement of air masses across temperature gradients as seen in advection fog. For instance, evaporation fog typically forms over bodies of water when moisture rises and interacts with cooler air, while radiation fog forms when the ground cools significantly at night. High humidity is a contributing factor in many types of fog but is not a defining characteristic of advection fog alone.