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Humidity & Condensation

Objectives:

    1.    Describe the three states in which water vapor can exist in the atmosphere.

    2.    Explain how air temperature affects the amount of water vapor air can contain.

    3.    Analyze how condensation occurs in the atmosphere.

Key Terms:

    water vapor    condensation    specific humidity    saturated    relative humidity    dew point    condensation nuclei

Notes: (18-1)

Humidity and condensation

Weather refers to the present state of the atmosphere & describes current conditions.  The amount of water vapor (humidity) in the atmosphere can greatly effect the severity of developing weather systems. 

Characteristics of Water

Water is the most unique substance on the face of the Earth.  It is the only substance that is present as a liquid, solid and gas at on the surface of the Earth.  Because of its unique properties all life revolves around the proximity of water and is theorized to have originated in it.

• solid - less than 0^oC - ice, snow, hail
• water - 0^oC to 100^oC - water, rain, clouds
• gas - greater that 100^oC - steam, humidity
• liquid to gas - vaporization, evaporation, transporation
• solid to gas - sublimation
• liquid to solid - freezing
• gas to solid - deposition
• gas to liquid - condensation

(www.uwsp.edu/.../ 02b_water_phase_change.gif)

(www.chemistry.wustl.edu/. ../PhaseChanges.jpg)

Humidity

At all times there are water molecules present in the atmosphere.  The water vapor is referred to as humidity.  Humidity is measured using a device called a psychrometer (type of hygrometer utilizing a wet and dry bulb).  It is important when describing humidity that you distinguish between specific and relative humidity.

• Humidity refers to the water vapor that is held between the air molecules

• Specific humidity is the amount of water being held in the air.

• As temp rises so does the amount of water vapor the air can hold (capacity doubles ~ every 11^oF)

• The amount of water vapor compared to the carrying capacity of a gas is called relative humidity

  • Value between 0-100%

  • At 100% it is said to be saturated

  • Any amount of additional water vapor is released as rain, dew, clouds, fog, etc...

  • The point of saturation may also be referred to as the dew point

(www.physicalgeography.net/ fundamentals/images...)