Geography; Humidity, Dew point, Clouds and Rainfall

  • Humidity –
    • Humidity capacity.
      • Capacity of air of certain volume at certain temperature to retain maximum amount of moisture content.
    • Absolute humidity.
      • Total weight of moisture content per unit volume of air at definite temperature.
    • Specific humidity.
      • Mass of the water vapors (grams) contained in a kg of air.
      • It represents the actual quantity of moisture present in a definite volume.
    • Relative humidity.
      • (Absolute humidity * 100 )/ Humidity capacity
  • Dew point – When relative humidity reaches 100%, the air is completely saturated. That air temperature is said to be the Dew point.
  • Fog –
    • Made from the droplets of water suspended in the lower of the atmosphere.
    • It is not considered as the form of precipitation.
    • Visibility of less than 1 km.
  • Smog – Smoke +Fog.
  • Haze –
    • Formed by the water particles that have condensed in the atmosphere.
    • Visibility lies between 1 km – 2 km.
  • Frost – Is the moisture on the ground that condenses directly into ice. (condensation below freezing point)
  • Clouds –
    • Mass of small water droplets or tiny ice crystals.
Latin namesThere meaning
CirrusLike feather, Very high clouds
CumulusLike heap, Flat base and rounded top
StratusLying in level sheets, Layer type
NimbusRain clouds
  • Classified according to their appearance, form and height:
    • High clouds. (6000 m to 12000 m)
      • Cirrus.
        • Contains small ice crystals.
        • White wispy and fibrous appearance.
      • Cirro Cumulus.
        • Contains ice crystals.
        • Rippled in appearance.
      • Cirro Stratus.
        • Appears like a thin white almost transparent sheet.
    • Middle clouds. (2100 m to 6000 m)
      • Alto Cumulus.
        • Contains droplets in layers and patches.
      • Alto Stratus.
        • Contains droplets forming sheets of grey or watering looking clouds.
    • Low clouds. (below 2100 m)
      • Strato Cumulus.
        • Large globular masses.
        • Bumpy looking.
        • Soft and grey in appearance.
        • And regular or wavy pattern.
      • Nimbo Stratus.
        • Dark grey and rainy looking.
        • Dense and shape less.
        • Often gives continuous rain.
      • Stratus.
        • Are low grey and layered.
        • Fog like in appearance.
        • Brings dull weather accompanied by drizzle.
    • Clouds with great vertical extent. (1500 m to 9000 m)
      • Cumulus.
        • Round top flat base.
        • A whitish grey globular mass.
        • Consists of individual cloud units.
      • Cumulo Nimbus.
        • Great vertical extent.
        • White or black globular masses.
        • Brings conventional rain and thunder.
  • Precipitation –
    • Classified on the basis of its origin.
      • Conventional rainfall.
        • Occurs due to thermal conventional currents caused due to insolational heating of ground surface.
        • Example: Congo basin, Amazon basin, South-east Asia etc.
      • Orographic rainfall.
        • Caused due to ascent of air forced by mountain barrier.
        • Example: Mahabaleshwar, Western Ghats (600 cm rainfall) etc.
      • Frontal rainfall.
        • Due to upward movement of air caused by convergence of cold air masses against warm air masses.
        • Example: North-west Europe (due to convergence of cold continental and warm oceanic air) etc.
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