Atmospheric Moisture

1
Atmospheric Moisture
CH 5. pp. 133-163
Saturated Air Air contains as much water vapor
as it possibly can
FIG 5-1 on p. 134
If Evaporation gt Condensation then,
Condensation will increase eventually
Evaporation Condensation
This state is called saturation
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2
Atmospheric Moisture
Humidity
1. VAPOR PRESSURE
The partial pressure exerted by water vapor

• Increase Temperature Increase pressure exerted
• Increase the concentration increase pressure
  exerted

2. ABSOLUTE HUMIDITY The density of water
vapor (g/m3)

• It is affected by atmospheric volume
• This is a drawback this is not widely used

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3
Atmospheric Moisture
Humidity
3. SPECIFIC HUMIDITY the mass of water vapor
existing in a given mass Of air (g of H2Ov/kg
of air)

• Affected by pressure
• Value does not change when air expands
• It is not temperature dependant
• It is more widely used in scientific community

• MIXING RATIO similar to specific humidity
  except the mass of water
• vapor is compared to the mass of dry air

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4
Atmospheric Moisture
Humidity

1. RELATIVE HUMIDITY this is what is most familiar

• Relates the amount of H2Ov in the air to the max
  possible

RH(specific humidity)/(saturation specific
humidity)100

• If you increase the temperature you increase the
  saturations
• specific humidity decrease RH
• Drawback cant compare humidity in two
  different locations

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5
Atmospheric Moisture
Humidity
6. DEW POINT The temperature at which
saturation can occur

• When the dew point is high there is a lot of
  water vapor in the air
• Dew point can NEVER exceed the air temperature

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6
Atmospheric Moisture
Methods of achieving saturation

1. Adding water vapor to the air
2. Mixing cold air with warm, moist air
3. Lowering the temperature to the dew point

Lets talk about 3
Air Temperature can change by Diabatic
Adiabatic Processes
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7
Atmospheric Moisture
Diabatic Processes
Processes that involve the removal/input of heat
Look at the first equation on p.153
Increase Heat Increase Temp. Increase volume
Adiabatic Processes
Processes that do not involve the removal/input
of heat
Look at the second equation on p.153
Expansion of air Increase volume Decreases
Temp.
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8
Atmospheric Moisture
LCL
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9
Atmospheric Moisture
Forms of condensation

• Dew
• 2. Frost
• 3. Frozen Dew
• 4. Fog

29 June 2007