Fog represents the collection of water droplets or ice crystals suspended in the air at or near the Earth’s surface. Fog is basically a low-lying cloud. The only difference between fog and mist is
their density. Fog reduces visibility to less than 1 km while mist reduces visibility to no less than
1 km.
                           Advection fog forms when warm, moist air horizontally moves over a cold surface, which
cools the air to its dew point. Advection fog can form any time, and can be very persistent. It is
common along coastlines where moist air moves from over the water to over the land, or when
an air mass moves over a cold surface (e.g., snow), and the moisture in the air condenses into fog
as the surface cools it. Advection radiation fog forms when warm, moist air moves over a cold
surface, which is cold as a result of radiation cooling. When warm, humid air moves over cold
water, it is called sea fog.
                            The most stable fogs occur when the surface is colder than the air above; that is, in the presence of a temperature inversion. Fogs also can occur when cold air moves over a warm, wet surface
and becomes saturated by the evaporation of moisture from the underlying surface. Convection
currents, however, tend to carry the fog upward as it forms, and it appears to rise as steam or
smoke from the wet surface. This is the explanation of steam fogs that are produced when cold
Arctic air moves over lakes, streams, inlets of the sea, or newly formed openings in the pack ice;
hence, the term Arctic sea smoke.

A Foggy Road


Post a Comment