Fog is a cloud that forms near ground level and reduces visibility. It is made up of tiny water droplets that form when water vapor in the air condenses onto small particles suspended in the atmosphere. Let’s learn about the different types of fog.
Types of fog
Radiation fog
Radiation fog typically forms during winter under calm and clear weather conditions. After sunset, the ground cools by radiating heat into the atmosphere. As the air near the surface cools, water vapor condenses onto condensation nuclei (tiny particles in the atmosphere), forming tiny water droplets that make up the fog.
The depth of the fog increases as cooling continues throughout the night. Radiation fog usually dissipates after sunrise, when the Sun warms the ground and the air temperature rises.
(Condensation nuclei: The particles suspended in the air e.g. dust on which the water vapor condenses.)
Advection fog
Advection fog forms when warm, moist air moves over a cooler surface, such as cold land or water. As the air cools to its dew point, water vapor condenses to form fog. Unlike radiation fog, advection fog can develop over both land and water and often persists during the day.
(Dew point temperature: The temperature at which air can hold no more water vapor.)
Steam fog
Steam fog forms over a warm water body when colder air moves across it. The warm, moist air just above the surface is cooled by the incoming cold air, causing the water vapor to condense and form fog.
Upslope fog
Upslope fog forms when moist air moves up along a mountain slope and cools.
Precipitation fog
This type of fog forms when rain falls from the warm air above a front into a colder air near the surface. The rain on the ground evaporates and saturates the cold air. Any further evaporation results in condensation and the formation of fog.
(Front: The boundary between two air masses of different properties.)
Freezing fog
When fog forms at temperatures below freezing, it is known as freezing fog. The water droplets remain in a liquid state (called supercooled liquid) until they come into contact with a surface, where they freeze upon impact.
(Also read: Types of Rainfall | Convectional, Orographic, and Cyclonic)
Fog vs mist vs haze
Fog and mist are both composed of tiny water droplets that form when water vapor condenses. Fog is denser than mist, with visibility reduced to less than 1,000 meters. In misty conditions, visibility is greater than 1,000 meters. Haze, on the other hand, is caused by small particles such as dust, smoke, or pollutants suspended in the air.
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