Humidity
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  • 1. Humidity
  • 2. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Humidity Humidity : the amount of water vapor in the air The maximum quantity of moisture that can be held in the air depends on air temperature
  • 3. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Humidity Relative Humidity : compares the amount of water vapor present in the air to the maximum amount that the air can hold at that temperature Expressed as a percentage: At 100% relative humidity, air is saturated.
  • 4. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Humidity
    • Relative Humidity changes when:
    • Atmosphere gains or loses water vapor
      • Evaporation
    • Temperature changes
      • Lower temperature  relative humidity rises
      • Raise temperature  relative humidity decreases
  • 5. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Humidity
    • Specific Humidity : actual quantity of water held by a parcel of air
    • Grams of water vapor per kilogram of air (g/kg)
    • Highest in equatorial zones
    • Lowest near poles
  • 6. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Dew-point temperature : temperature at which air with a given humidity will reach saturation when cooled without changing its pressure Humidity
  • 7. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. The Adiabatic Process
    • Adiabatic Principle : the physical principle that a gas cools as it expands and warms as it is compressed
    • Change in temperature:
    • caused only by a change in pressure
    • not caused by heat flowing in or out of the gas
  • 8. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. The Adiabatic Process As a parcel of air rises  pressure on the parcel decreases  air expands and cools As a parcel of air descends  pressure on the parcel increases  air is compressed and warms Atmospheric pressure decreases with altitude so...