GEOG 1101 Lecture Notes - Lecture 9: Fog, Ice Fog, Radiative Cooling

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Radiation fog is produced over land as the ground emits LW radiation, thus losing heat energy and
cooling. This cools the air in contact with the ground and if the air Tº drops to the d.p.Tº, then
condensation may occur. This process is known as radiational cooling.
* This type of fog is also called ground fog. This the most common
type of fog which forms the Athens, GA area.
* If it forms in a mountainous area, then it may be called valley fog.
This occurs as cold, heavy air drains downhill (cold air drainage).
* It forms best on calm, clear nights in late fall & winter and is
usually deepest around sunrise.
Advection fog occurs when warm, moist air moves over a colder surface and the air cools to its
d.p.T. This is most common as warm air from off a large water surface
(ocean, gulf) moves over the colder, coastal land.
* remember that advection means the horizontal movement of air
* This type fog is usually associated with winds of 5 - 15 mph &
is often 300 - 600 m thick.
EX: West Coast of U.S. (San Francisco area), Gulf of Mexico
coastal area, and the Midwest U.S. especially in winter.
* For some coastal deserts (Atacama in S.A., Namib in Africa),
advection fog may be the only moisture they receive.
* Ice fog is a type of advection fog which may form in cold polar areas, where the fog droplets
freeze and form ice droplets
Upslope fog forms as warm, moist air flows up along an elevated plain,
or mountain range. The air Tº reaches d.p.Tº by adiabatic cooling
as it rises.
EX: Western Great Plains of the U.S. along the eastern side of
the Rocky Mountains.
Evaporation fog forms when the air reaches saturation (d.p.T = air temperature) by having water
vapor added to it and not by lowering of the air temperature. In other words, liquid water evaporates
into the air parcel from off a water body or wet surface.
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