:For the abbreviation, see FOG For the B-Side by Radiohead see Fog (song).
Early morning fog obscures the surface of this lake in Carrollton, Georgia, but the sky remains clear.
Fog is cloud in contact with the ground.It occurs when moisture form the surface of the Earth evaporates; as this evaporated moisture moves upward, it cools and condenses into the familiar phenomenon of fog. Fog differs from clouds in that fog touches the surface of the Earth, while clouds do not. It can form in a number of ways, depending on how the cooling that caused the condensation occurred:
- Advection fog occurs when moist air passes over cool ground by advectionFluid dynamics Advection is the transport of a conserved scalar quantity that is transported in a vector field. A good example to have in mind would be the transport of pollution in a river: the motion of the water carries the polluted water downstream (s ( windFor the 1928 film, see The Wind. Wind in the most general sense, is the movement of air. It occurs at all scales, from local breezes generated by heating of land surfaces and lasting tens of minutes to global winds resulting from solar heating of the plan) and is cooled. This form is most common at seaSunset at sea A sea (pronounced see is a large expanse of saline water connected with an ocean. The term is also used for large, usually saline, lakes that lack a natural outlet, such as the Caspian Sea and the Dead Sea. The Sea of Galilee is a small fres when tropical air encounters cooler higher- latitudeLatitude denoted φ, gives the location of a place on Earth north or south of the Equator. Latitude is an angular measurement ranging from 0° at the Equator to 90° at the poles. Usually, the difference in latitude largely affects the climate and/or wea waterDrinking water This article focuses on water as we experience it every day. The water (molecule) article describes water from a scientific and technical perspective. Water is an abundant substance on Earth. It exists in many forms, such as sea, rain, ands. It is also extremely common as a warm front passes over an area with significant snowpack .
- Steam fog is the most localized form and is created by cold air passing over much warmer water. The air is quickly saturated by evaporationEvaporation is the process whereby atoms or molecules in a liquid state (or solid state if the substance sublimes) gain sufficient energy to enter the gaseous state. The thermal motion of a molecule must be sufficient to overcome the surface tension of th and the condensation thus created is seen as wispy steam. Steam fog is most common in polar regions, and around deeper and larger lakes in late autumn and early winter. It is closely related to lake-effect snow and lake-effect rain , and often causes freezing fog, or sometimes hoar frost.
Evening fog obscures London's Tower Bridge from passers by.
- Precipitation fog (or frontal fog) forms as precipitation falls into drier air below the cloud, the liquid droplets evaporate into water vapour. The water vapour cools and increases the moisture content of the air. As the air saturates below the cloud, fog forms.
- Upslope fog forms when winds blow air up a slope (called orographic lift), adiabatical cooling it as it rises, and causing the moisture in it to condense. This often causes freezing fog on mountaintops, where the cloud ceiling would not otherwise be low enough.
- Valley fog forms in mountain valleys, often during winter. It is the result of a temperature inversion caused by heavier cold air settling into the valley, with warmer air passing over the mountains above. It is essentially radiation fog confined by local topology, and can last for several days in calm conditions.
Ice fog permiates Winnipeg on a -35°C February day from nearly any moisture at all, from cars, homes, or industry.
- Freezing fog is when liquid fog droplets freeze to surfaces, forming white rime ice. This is very common on mountaintops which are exposed to low clouds. It is equivalent to freezing rain, and essentially the same as the ice which forms inside a freezer which is not of the "frostless" or "frost-free" type.
All types of fog form when the relative humidity reaches 100%, and the air temperature tries to drop below the dewpoint, pushing it lower by forcing the water vapor to condense.
Fog reduces visibility . Some vehicles have radar etc., cars have to drive slower and use more lights. Especially dangerous is when fog is very localized, and the driver is caught by surprise.
