Definition - What does Advection Fog mean?
Advection Fog is a type of fog that is formed due to the slow passage of a relatively warm, moist, stable air over a colder surface. The surface can be land or a water mass, each cooler than the warm and more humid air moving horizontally above it. This type of fogs often appears to roll into an area and have a forward movement.
Petropedia explains Advection Fog
Whenever cold and warm ocean currents are in close proximity they affect the adjacent coasts. A good example is provided by the frequent dense fogs formed off the Grand Banks of Newfoundland in summer, when winds from the warm Gulf Stream blow over the cold Labrador Current. It also may occur over land, especially in winter when warm air blows over frozen or snow-covered ground. Advection fogs occur when the winds are:
- blowing at a speed of 5 meters per second (10 miles per hour);
- light to maintain a temperature contrast between air and surface; and
- not strong enough to produce turbulent mixing through a considerable depth of the atmosphere.