Fog is a visible mass consisting of cloud water droplets or ice crystals suspended in the air at or near the Earth’s surface. Fog can be considered a type of low-lying cloud and is heavily influenced by nearby bodies of water, topography, and wind conditions. In turn, fog has affected many human activities, such as shipping, travel, and warfare. It is serene, calming and sometimes spiritual too. But you definitely didn’t distinguish one from the other.
The only difference between mist and fog is visibility. The phenomenon is called fog, if the visibility is one kilometre (1,100 yards) or less. Otherwise it is known as mist. Seen from a distance, mist is bluish, and haze is more brownish. We are talking fogs this time though.
1. Radiation Fog
It is formed by the cooling of land after sunset by thermal radiation in calm conditions with clear sky. The cool ground produces condensation in the nearby air by heat conduction. In perfect calm the fog layer can be less than a meter deep but turbulence can promote a thicker layer. Radiation fogs occur at night, and usually do not last long after sunrise, but they can persist all day in the winter months especially in areas bounded by high ground such as the Vale of York in England. Radiation fog is most common in autumn and early winter. Examples of this phenomenon include the Tule fog.
2. Advection Fog
This occurs when moist air passes over a cool surface by advection (wind) and is cooled. It is common as a warm front passes over an area with significant snow-pack. It is most common at sea when moist air encounters cooler waters, including areas of cold water upwelling, such as along the California coast.
4. Evaporation fog
Also called steam fog, it forms over bodies of water overlain by much colder air; this situation can also lead to steam devils forming. Lake effect fog is of this type, sometimes in combination with other causes like radiation fog. It tends to differ from those over land in that it is, like lake-effect snow, a convective phenomenon, resulting in fog which can be quite a bit denser, deeper, and looks fluffy from above. Most other fog is stratiform; steam devils, which look like their dust counterparts, are often seen in this situation.
5. Ice fog
Ice fog forming in very low temperatures can be the result of other mechanisms mentioned here, as well as the exhalation of moist warm air by herds of animals. It can be associated with the diamond dust form of precipitation, in which very small crystals of ice form and slowly fall. This often occurs during blue sky conditions which can cause many types of halos and other results of refraction of sunlight by the airborne crystals.
6. Freezing fog
When water droplets in fog are cooled below the freezing point, they remain in a liquid state (unless they fall to extreme frigid lows). When these droplets hit a freezing surface, the result is white rime. These feathery ice crystals coat everything and magically transform the world into a winter wonderland.
In the West, freezing fog is often referred to as “pogonip,” the Shoshone word for “cloud.”
7. Upslope fog
This is the fog you see artfully draped over hills and mountains. Upslope fog forms when moist air is going up the slope of a mountain or hill which condenses into fog on account of adiabatic cooling, and to a lesser extent the drop in pressure with altitude.