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Atmospheric Moisture

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 > Condensation then,. Condensation will increase & eventually. Evaporation = Condensation. This state is called “saturation”. 29 June 2007.

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Atmospheric Moisture

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  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 > Condensation then, Condensation will increase & eventually Evaporation = Condensation This state is called “saturation” 29 June 2007

  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 29 June 2007

  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 29 June 2007

  4. Atmospheric Moisture Humidity • 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: can’t compare humidity in two different locations 29 June 2007

  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 29 June 2007

  6. Atmospheric Moisture Methods of achieving saturation • Adding water vapor to the air • Mixing cold air with warm, moist air • Lowering the temperature to the dew point Let’s talk about #3 Air Temperature can change by : Diabatic & Adiabatic Processes 29 June 2007

  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. 29 June 2007

  8. Atmospheric Moisture LCL 29 June 2007

  9. Atmospheric Moisture Forms of condensation • Dew • 2. Frost • 3. Frozen Dew • 4. Fog 29 June 2007

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