CH. 17 – MOISTURE
Changes of State of Water <ul><li>Heat = energy  </li></ul><ul><li>Adding heat to an object makes atoms vibrate faster </l...
Change of State of Water <ul><li>Latent heat – energy added to or released by substance w/out changing temperature  </li><...
Humidity <ul><li>Describes amount of water vapor in air </li></ul><ul><li>- water vapor sits in spaces between dry air gas...
Dry Air Analysis (consistent worldwide) <ul><li>Nitrogen  =  78% </li></ul><ul><li>Oxygen (O 2 ) =  21% </li></ul><ul><li>...
Water Vapor Capacity Table <ul><li>Temperature dependent </li></ul><ul><li>Hotter air = molecules moving farther apart = m...
Relative Humidity <ul><li>- measures how close air is to saturation w/ water vapor </li></ul><ul><li>- expressed as a perc...
Relative Humidity <ul><li>Mixing ratio  </li></ul><ul><li>- actual amount water vapor by weight in one kg of air </li></ul>
Examples of humidity problems <ul><li>Temp  ( o C)   M.R.  (g)  R.H. </li></ul><ul><li>1.  25   4    ? </li></ul><ul><li>2...
True or False? <ul><li>Air with a higher relative humidity has more water vapor in it than air with a lower relative humid...
January Temperatures <ul><li>50% RH in Siberia </li></ul><ul><li>30% RH in Australia </li></ul>
Relative Humidity <ul><li>Question: </li></ul><ul><li>If temp. increases w/out changing the mixing ratio, what happens to ...
Factors that change relative humidity <ul><li>1) Change in air temperature </li></ul><ul><li>Assuming no change in mixing ...
Rel. hum. vs. temp
Factors that change relative humidity <ul><li>2) Change amount of water vapor </li></ul><ul><li>a) Add water vapor through...
Dew Point <ul><li>Temperature at which air is saturated without changing the mixing ratio </li></ul><ul><li>- air has to _...
Examples of humidity problems <ul><li>Temp  ( o C)   M.R.  (g)  R.H.  </li></ul><ul><li>1.  25   4    20% </li></ul><ul><l...
Condensation in the atmosphere <ul><li>On surface = dew </li></ul><ul><li>Above surface = fog </li></ul><ul><li>Aloft = cl...
Necessary conditions for condensation <ul><li>1) Saturated Air (air at dew point) </li></ul><ul><li>2) Condensation Nuclei...
Saturated air <ul><li>Two methods for cooling air to dew point: </li></ul><ul><li>1) Environmental Lapse Rate </li></ul><u...
Cooling to Dew Point: Method #2 <ul><li>2) Adiabatic Temp. Change </li></ul><ul><li>- caused by changing air’s volume </li...
Adiabatic Temperature Changes <ul><li>Air expands = temp. decreases </li></ul><ul><li>Ex:  aerosol spray can </li></ul><ul...
Cloud Formation <ul><li>As air rises, it expands & cools </li></ul><ul><li>Dry adiabatic rate = cooling of unsaturated air...
Condensation <ul><li>Latent heat released by water vapor </li></ul><ul><li>Ex:  In summer, can “sweats” </li></ul><ul><li>...
Cloud Formation <ul><li>Wet adiabatic rate = cooling of saturated air </li></ul><ul><li>- always < 10 o  C   per km </li><...
Review cloud forming process: <ul><li>1.  Air rises </li></ul><ul><li>2. Air expands </li></ul><ul><li>3. Air cools adiaba...
Review cloud forming process: <ul><li>4. Air reaches dew point </li></ul><ul><li>altitude varies based on how much water v...
Review cloud forming process: <ul><li>* Key to cloud formation is to get large amounts of air to rise! </li></ul>
Mechanisms forcing air to rise: <ul><li>1) Orographic Lifting - physical barrier to wind </li></ul><ul><li>Clouds form on ...
Orographic Lifting <ul><li>“ Rain shadow” deserts on leeward side of mountains </li></ul><ul><li>Ex:  Basin & Range in Nev...
 
Mechanisms forcing air to rise: <ul><li>2) (hot air rises) </li></ul><ul><li>LocaConvective lifting lly, caused by intense...
Mechanisms forcing air to rise: <ul><li>3) Convergence </li></ul><ul><li>Surface air moves from high pressure to low press...
Mechanisms forcing air to rise: <ul><li>4) Frontal Wedging </li></ul><ul><li>Cool air acts as a barrier forcing warmer air...
Frontal Wedging <ul><li>Major factor in Midwest </li></ul><ul><li>- warm moist air (Gulf of Mexico) </li></ul><ul><li>- co...
Fog <ul><li>Cloud with its base at or very near the ground </li></ul><ul><li>Ex:  Radiation fog (ground fog) </li></ul><ul...
Radiation Fog <ul><li>Air above ground cools rapidly to dew point  </li></ul><ul><li>- after sunrise, fog evaporates from ...
Air Stability <ul><li>Causes difference in cloud development </li></ul><ul><li>Ex:  gray layered clouds vs. thunderheads <...
Stable Air <ul><li>Air resists vertical displacement </li></ul><ul><li>- air at surface is colder than temp. of surroundin...
Unstable Air <ul><li>Air that does not resist vertical displacement </li></ul><ul><li>- air at surface is warmer than surr...
Weather Conditions  <ul><li>Stable Air: </li></ul><ul><li>a) Characteristically sheet-like layered clouds (stratus) </li><...
Stratus clouds
Weather with stable air: <ul><li>c) Other phenomena: </li></ul><ul><li>- poor visibility & haze </li></ul><ul><li>- fog, s...
Inversions
Weather Conditions <ul><li>Unstable Air: </li></ul><ul><li>a) Clouds w/ considerable vertical development </li></ul><ul><l...
Cloud of vertical development
<ul><li>c) Good visibility except during rain </li></ul>
Weather w/unstable air <ul><li>d) Extreme weather phenomena: </li></ul><ul><li>- lightning & thunder </li></ul><ul><li>- h...
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Ch17_Moisture_students

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Ch17_Moisture_students

  1. 1. CH. 17 – MOISTURE
  2. 2. Changes of State of Water <ul><li>Heat = energy </li></ul><ul><li>Adding heat to an object makes atoms vibrate faster </li></ul><ul><li>Heat ≠ temperature! </li></ul><ul><li>Temperature = average of all molecular motion </li></ul>
  3. 3. Change of State of Water <ul><li>Latent heat – energy added to or released by substance w/out changing temperature </li></ul><ul><li>Latent = “hidden” </li></ul><ul><li>Ex: Beaker w/ ice and water </li></ul>
  4. 4. Humidity <ul><li>Describes amount of water vapor in air </li></ul><ul><li>- water vapor sits in spaces between dry air gases </li></ul><ul><li>Saturation = spaces filled to capacity w/ water vapor </li></ul>
  5. 5. Dry Air Analysis (consistent worldwide) <ul><li>Nitrogen = 78% </li></ul><ul><li>Oxygen (O 2 ) = 21% </li></ul><ul><li>Argon = <1% </li></ul><ul><li>Carbon Dioxide = 0.035% </li></ul><ul><li>TOTAL 100% </li></ul>
  6. 6. Water Vapor Capacity Table <ul><li>Temperature dependent </li></ul><ul><li>Hotter air = molecules moving farther apart = more space for water vapor </li></ul>
  7. 7. Relative Humidity <ul><li>- measures how close air is to saturation w/ water vapor </li></ul><ul><li>- expressed as a percentage </li></ul><ul><li>- is temperature dependent! </li></ul>
  8. 8. Relative Humidity <ul><li>Mixing ratio </li></ul><ul><li>- actual amount water vapor by weight in one kg of air </li></ul>
  9. 9. Examples of humidity problems <ul><li>Temp ( o C) M.R. (g) R.H. </li></ul><ul><li>1. 25 4 ? </li></ul><ul><li>2. 10 3.5 ? </li></ul>
  10. 10. True or False? <ul><li>Air with a higher relative humidity has more water vapor in it than air with a lower relative humidity? </li></ul>
  11. 11. January Temperatures <ul><li>50% RH in Siberia </li></ul><ul><li>30% RH in Australia </li></ul>
  12. 12. Relative Humidity <ul><li>Question: </li></ul><ul><li>If temp. increases w/out changing the mixing ratio, what happens to relative humidity? </li></ul>
  13. 13. Factors that change relative humidity <ul><li>1) Change in air temperature </li></ul><ul><li>Assuming no change in mixing ratio: </li></ul><ul><li>Increase temp. = __________ RH </li></ul><ul><li>Decrease temp. = _________ RH </li></ul>
  14. 14. Rel. hum. vs. temp
  15. 15. Factors that change relative humidity <ul><li>2) Change amount of water vapor </li></ul><ul><li>a) Add water vapor through </li></ul><ul><li>____________ </li></ul><ul><li>b) Remove water vapor by </li></ul><ul><li>____________ </li></ul>
  16. 16. Dew Point <ul><li>Temperature at which air is saturated without changing the mixing ratio </li></ul><ul><li>- air has to ________to reach dew point </li></ul>
  17. 17. Examples of humidity problems <ul><li>Temp ( o C) M.R. (g) R.H. </li></ul><ul><li>1. 25 4 20% </li></ul><ul><li>2. 10 3.5 50% </li></ul><ul><li>What is dew point of Example 2? </li></ul>
  18. 18. Condensation in the atmosphere <ul><li>On surface = dew </li></ul><ul><li>Above surface = fog </li></ul><ul><li>Aloft = clouds </li></ul>
  19. 19. Necessary conditions for condensation <ul><li>1) Saturated Air (air at dew point) </li></ul><ul><li>2) Condensation Nuclei </li></ul><ul><li>Ex: dust, salt, smoke, ash </li></ul><ul><li>“ hygroscopic particles” </li></ul>
  20. 20. Saturated air <ul><li>Two methods for cooling air to dew point: </li></ul><ul><li>1) Environmental Lapse Rate </li></ul><ul><li>- air is cooler the further you are from Earth’s surface </li></ul><ul><li>- rate changes daily </li></ul>
  21. 21. Cooling to Dew Point: Method #2 <ul><li>2) Adiabatic Temp. Change </li></ul><ul><li>- caused by changing air’s volume </li></ul><ul><li>* No heat (energy) is added or removed from the air! </li></ul>
  22. 22. Adiabatic Temperature Changes <ul><li>Air expands = temp. decreases </li></ul><ul><li>Ex: aerosol spray can </li></ul><ul><li>Air compresses = temp. increases </li></ul><ul><li>Ex: bicycle tire pump heating up </li></ul>
  23. 23. Cloud Formation <ul><li>As air rises, it expands & cools </li></ul><ul><li>Dry adiabatic rate = cooling of unsaturated air </li></ul><ul><li>- constant 10 o C per km </li></ul>
  24. 24. Condensation <ul><li>Latent heat released by water vapor </li></ul><ul><li>Ex: In summer, can “sweats” </li></ul><ul><li>- latent heat warms can </li></ul>
  25. 25. Cloud Formation <ul><li>Wet adiabatic rate = cooling of saturated air </li></ul><ul><li>- always < 10 o C per km </li></ul><ul><li>Varies depending on amount of condensation in cloud </li></ul><ul><li>(latent heat warms surrounding air) </li></ul>
  26. 26. Review cloud forming process: <ul><li>1. Air rises </li></ul><ul><li>2. Air expands </li></ul><ul><li>3. Air cools adiabatically </li></ul>
  27. 27. Review cloud forming process: <ul><li>4. Air reaches dew point </li></ul><ul><li>altitude varies based on how much water vapor is in rising air </li></ul><ul><li>5. Condensation begins </li></ul>
  28. 28. Review cloud forming process: <ul><li>* Key to cloud formation is to get large amounts of air to rise! </li></ul>
  29. 29. Mechanisms forcing air to rise: <ul><li>1) Orographic Lifting - physical barrier to wind </li></ul><ul><li>Clouds form on windward side of mountain </li></ul><ul><li>As air descends, it compresses & heats up adiabatically </li></ul>
  30. 30. Orographic Lifting <ul><li>“ Rain shadow” deserts on leeward side of mountains </li></ul><ul><li>Ex: Basin & Range in Nevada </li></ul>
  31. 32. Mechanisms forcing air to rise: <ul><li>2) (hot air rises) </li></ul><ul><li>LocaConvective lifting lly, caused by intense heating on summer afternoons </li></ul><ul><li>- forms cumulus clouds </li></ul>
  32. 33. Mechanisms forcing air to rise: <ul><li>3) Convergence </li></ul><ul><li>Surface air moves from high pressure to low pressure (wind) </li></ul>
  33. 34. Mechanisms forcing air to rise: <ul><li>4) Frontal Wedging </li></ul><ul><li>Cool air acts as a barrier forcing warmer air to rise </li></ul><ul><li>Regional cause of clouds </li></ul>
  34. 35. Frontal Wedging <ul><li>Major factor in Midwest </li></ul><ul><li>- warm moist air (Gulf of Mexico) </li></ul><ul><li>- cold dry air (Canada) </li></ul>
  35. 36. Fog <ul><li>Cloud with its base at or very near the ground </li></ul><ul><li>Ex: Radiation fog (ground fog) </li></ul><ul><li>- fairly clear nights w/ high relative humidity </li></ul>
  36. 37. Radiation Fog <ul><li>Air above ground cools rapidly to dew point </li></ul><ul><li>- after sunrise, fog evaporates from ground up (“lifts”) </li></ul>
  37. 38. Air Stability <ul><li>Causes difference in cloud development </li></ul><ul><li>Ex: gray layered clouds vs. thunderheads </li></ul>
  38. 39. Stable Air <ul><li>Air resists vertical displacement </li></ul><ul><li>- air at surface is colder than temp. of surrounding air </li></ul><ul><li>- Force air to rise </li></ul><ul><li>Ex: Orographic lifting </li></ul>
  39. 40. Unstable Air <ul><li>Air that does not resist vertical displacement </li></ul><ul><li>- air at surface is warmer than surrounding air </li></ul><ul><li>- begins and continues to rise on its own (ex: “convective lifting”) </li></ul>
  40. 41. Weather Conditions <ul><li>Stable Air: </li></ul><ul><li>a) Characteristically sheet-like layered clouds (stratus) </li></ul><ul><li>Ppt.- producing = nimbostratus </li></ul><ul><li>b) light to moderate ppt. of long duration </li></ul>
  41. 42. Stratus clouds
  42. 43. Weather with stable air: <ul><li>c) Other phenomena: </li></ul><ul><li>- poor visibility & haze </li></ul><ul><li>- fog, sleet, glaze </li></ul><ul><li>- inversions (smog alerts) </li></ul>
  43. 44. Inversions
  44. 45. Weather Conditions <ul><li>Unstable Air: </li></ul><ul><li>a) Clouds w/ considerable vertical development </li></ul><ul><li>b) Short episodes of heavy ppt. </li></ul><ul><li>(cumulonimbus clouds) </li></ul>
  45. 46. Cloud of vertical development
  46. 47. <ul><li>c) Good visibility except during rain </li></ul>
  47. 48. Weather w/unstable air <ul><li>d) Extreme weather phenomena: </li></ul><ul><li>- lightning & thunder </li></ul><ul><li>- hail </li></ul><ul><li>- tornadoes </li></ul><ul><li>- hurricanes </li></ul>

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