Condensation
• conversion from gaseous to either liquid or solid state
(in which case it is also called deposition).
• Two conditions are necessary:
ü
Availability of
hygroscopic nuclei,
ü
Relative Humidity greater than 100%.
Any surface, such as aerosols, plant leafs, etc. can act as condensation nuclei. Cooling of air column below its dew point temperature or addition of water above the holding capacity of air column develops saturation. E.g. Clouds, fog, dew. Precipitation is the process of falling of moisture from the base of cloud in different forms like rain, snow and hail. Various types of precipitation are‐
1. Convectional (convective rise of warm air),
2. Orographic (Rise caused by mountain barrier), and
3. Frontal.
Forms of condensation demarcated on the basis of location of condensation.
a) At ground: In winter season, long winter nights facilitate contact cooling. The cooling of the moist air column below its dew point temperature makes the ground object as hygroscopic nuclei facilitating condensation. This category
includes dew and frost.
Dew‐
Ø typical to lower latitudinal and altitudinal locations.
Ø eposited water droplets. (Dew point temperature: the temperature to which moist air is cooled at constant pressure and at constant water vapor to reach saturation with respect to water).
Frost‐
Ø deposited minute ice‐crystals.
Ø in higher latitudes and altitudinal areas where temperature is below the freezing point of water. (Frost point temperature: the temperature to which moist air is cooled at constant pressure and at constant water vapor to reach saturation with respect to ice).
b) Near ground condensation
Fog‐
Ø simply a ground level cloud.
Ø visible aggregate of suspended ice‐crystals and water droplets.
Ø Various types of fog are radiation, advection, frontal fog etc.
c) Atmospheric condensation: The condensation form that develops throughout the year and throughout the world barring the exception of extreme Polar Regions is clouds. Clouds can be defined as the visible aggregate of the tiny ice crystals and minute water droplets.
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