in fog-prone area
definition of fog
The term fog means a meteorological phenomenon caused by condensation of water vapor near the surface when the visibility is limited to less than 1km. The air in the fog feels humid and cold, and the relative humidity is close to 100%.
Fogs are classified as radiation fog, advection fog, upslope fog, frontal fog, and steam fog, depending on the cooling of air mass and the generation of water vapor sources.
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The fog that occurs on land as the sun sets and the ground cools on a clear night is radiation fog. It occurs well at night when there is no wind and relative humidity is high, and it occurs well on clear nights after rain. It occurs a lot within an hour of sunrise, and usually disappears within an hour or two after sunrise.
1. RADIATION FOG
2. ADVECTION FOG
Advection fogs form when relatively warm, moist air moves horizontally over a cooler surface. As the air passes over the cooler surface, it transfers heat downward causing it to cool diabatically. Advection fogs can be advected for considerable distances and persist well downwind of the area over which they form. They can have thicknesses up to about a half kilometer.
3. UPSLOPE FOG
Of all types of fog caused by the cooling of air, only upslope fog is formed by adiabatic cooling. When air flows along a gently sloping surface and atmospheric pressure decreases at higher altitudes, the rising air expands and consequently leads to cooling. Then the air cools and saturates to form fog.
4. FRONTAL FOG
Frontal fog forms near a front when raindrops, falling from relatively warm air above a frontal surface, evaporate into cooler air close to the Earth’s surface and cause it to become saturated.
5. STEAM FOG
Steam fog is commonly seen in lake. It forms during the fall season. As summer ends, water temperatures don't cool right away but
air temperature does.
As a mass of dry, cold air moves over a warmer lake the warm lake conducts warm, moist air into the air mass colder above and cause steam fog.
fog versus others
Fog versus Mist
Fog is not the same thing as mist. Fog is denser than mist. This means fog is more massive and thicker than mist. There are more water molecules in the same amount of space in a fog. Fog cuts visibility down to one kilometer, meaning it will prevent you from seeing further away than one kilometer from where you’re standing. Mist can reduce visibility to between one and two kilometers.
Fog versus clouds
Fog is similar to clouds, but the difference is called fog if the base is less than 1km away from the earth's surface, and clouds if the fog is located at the foot of the mountain, but it becomes fog for hikers.