Condensation is the phase transformation of water vapour to
liquid water. Water does not easily condense without a surface present. Vegetation,
soil, buildings provide surface for dew and frost formation. Particles act as
sites for cloud and fog drop formation.
Types of Condensation
1.
Clouds — When the moist air moves upward it cools down. When the temperature of
the air reaches the dew point, the water vapours condense in the form of small
droplets of water or ice crystals. These droplets cling to the dust particles
and hang in the air in the form of clouds. They move hither and thither along
the wind in the sky. Clouds are of a great variety depending on their height.
2.
Fog — Fog is formed in the same way as clouds with the only difference that fog
is formed near the surface of the earth or water bodies. It is formed when the
moist air cools down below its dew point in the lower layers of the atmosphere.
Fog is formed over the water when a cold current meets the hot current. Fogs
are clouds in contact with the ground. Several
types of fogs commonly form a) Radiation fog
b) Advection fog c) Up-slope fog d) Evaporation (mixing) fog.
3.
Dew — At night everything radiates heat which it had absorbed during the day. Grass,
flowers and leaves of trees radiate heat more quickly than ;r things because
they are good radiators. Thus, they become cold quite early. When the warm and
moist air comes into contact with them its moisture condenses into small
droplets of water on the grass and other things. These droplets arc- known as
dew. It occurs only on calm, cold and clear nights. The dew point is the
temperature at which the air is saturated with water vapour If a surface cools
below the dew point, water condenses on the surface and dew drops are formed. Dew
does not “fall”.
4.
Frost — If the dew-drops get frozen due to fall in temperature, it is called
the frost. It happens when the dew point is below the freezing point. On the
other hand, in dew formation, the dew point is above the freezing point.
If the temperature is below freezing, the dew
point is called the frost point. If the surface temperature falls below the
frost point water vapour is deposited directly as ice crystals called deposition.
When the dew-point temperature is less
than 0C, then we call this the "frost point". Frost will form when
the dew-point is less than 0 C because the temperature of the surface and near
the surface can be at or below freezing (0 C) thus, if moist air comes in
contact with that surface, we’ll get frost instead of dew! ( Difference between
Dew & Frost)
Advertisements
No comments:
Post a Comment