Which type of fog forms on calm, clear nights?

Radiation fog forms on calm, clear nights due to the cooling of the ground and the air in contact with it. When the ground loses heat rapidly during the night, it cools down the air directly above, causing the moisture in that layer of air to condense into tiny water droplets, which creates fog. This type of fog typically occurs in low-lying areas where cold air can settle, and because it relies on clear skies for effective radiative cooling, the presence of clouds or wind can prevent its formation.

In contrast, advection fog develops when warm, moist air moves over a cooler surface, causing the moisture to condense. Ice fog occurs in extremely cold conditions, where water vapor sublimates directly into ice crystals. Steam fog, on the other hand, forms when cold air moves over warmer water, leading to the evaporation of water and subsequently cooling to form fog. These processes differ significantly from the cooling mechanism involved in radiation fog formation, which is specifically associated with calm and clear nighttime conditions.