What process commonly caused fog to form at sea?

The formation of fog at sea is primarily influenced by the process of advection. Advection fog occurs when warm, moist air moves over cooler ocean waters, which causes the air temperature to drop and the moisture within the air to condense into tiny water droplets, forming fog. This type of fog is especially common in coastal areas where warm air from land meets the colder air above the sea.

The cooling of the air is crucial in this process, as it allows the air to reach its dew point, the temperature at which it can no longer hold all of its moisture, leading to condensation and fog formation. This is distinct from processes such as radiation (which pertains to cooling at night), convection (which involves vertical mixing of air), and simple condensation (which could happen in various scenarios but does not specifically describe the movement of warm air over cooler surfaces). Advection, therefore, is the key mechanism in the formation of fog at sea, making it the correct answer.