Chapter 7 Water and Atmospheric Moisture

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Chapter 7Water and Atmospheric Moisture

• Geosystems 6e
• An Introduction to Physical Geography

Robert W. Christopherson Charles E. Thomsen
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Water and Atmospheric Moisture

• TOPICS
• Adiabatic Processes
• Atmospheric Stability 
• Clouds 
• Fog  

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Adiabatic Processes  

• Adiabatic processes
• Begins with a parcel of air
• Bouyancy caused initially by differences in
  (near) surface temperature
• Less dense, warmer air rises, more dense, colder
  air sinks, after which
• Ascending or descending air will undergo changes
  in temperature with no exchange of heat. This is
  an adiabatic process.

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Buoyancy
Figure 7.15
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Adiabatic Processes  

• Adiabatic processes
• Normal lapse rate the average decrease in
  temperature with increasing altitude
• Environmental lapse rate the actual lapse rate
  at a particular place and time
• Ascending or descending air will undergo changes
  in temperature with no exchange of heat. This is
  an adiabatic process.
• Heat WAS exchanged diabatic process.

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Adiabatic Processes
Figure 7.17
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Adiabatic Processes  

• Dry adiabatic rate (DAR)
• Also called the Dry Adiabatic Lapse Rate (DALR)
• 10 C/ 1000 m
• 5.5 F/ 1000 ft
• Lifting Condensation Level (LCL) is reached,
  then
• Moist adiabatic rate (MAR)
• Also called the Wet Adiabatic Lapse Rate (WALR)
• 6 C/ 1000 m
• 3.3 F/ 1000 ft

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AtmosphericStability
Figure 7.20
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Atmospheric Stability  

• Stable and unstable atmospheric conditions
• Involves a parcel of air and its surrounding
  environment in the atmosphere
• Stable atmosphere
• A parcel of air is discouraged from rising
• Kind of weather normally associated?
• Unstable atmosphere
• A parcel of air is encouraged to rise
• Kind of weather normally associated?

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 Examples of Stability
 Unstable AtmosphereParcel of air is encouraged
to rise
Figure 7.20
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 Examples of Stability
 Stable AtmosphereParcel of air is discouraged
from rising
Figure 7.20
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Atmospheric Stability  

• To determine atmospheric stability
• Compare the ELR with the DAR (or DALR) and MAR
  (or WALR)
• If ELR lt MAR lt DAR STABLE
• If ELR gt DAR gt MAR UNSTABLE
• If MAR lt ELR lt DAR CONDITIONALLY UNSTABLE

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Atmospheric Stability  

• For example
• We measure and find the ELR to be 12 Cº/ 1000 m
• We know the DAR is 10 Cº/ 1000 m.
• We know the MAR is 6 Cº/ 1000 m.
• If ELR (12) gt DAR (10) gt MAR (6) then?
• If ELR gt DAR gt MAR UNSTABLE

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Atmospheric Stability  

• If ELR is large (shallow slope), it will be to
  the left of both the DAR and MAR lines
• This describes unstable atmospheric conditions!
• If ELR is small (steep slope), it will be to the
  right of both the DAR and MAR lines.
• This describes stable atmospheric conditions!

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Atmospheric Temperatures and Stability
Figure 7.19
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Moisture Droplets
Figure 7.20
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Raindrop and Snowflake Formation
Collision-coalescence process
Figure 7.22
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Cloud Types and Identification  
Figure 7.23
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Cirrus
Figure 7.23
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Cirrostratus
Figure 7.23
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Cirrocumulus
Figure 7.23
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Altocumulus
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Altostratus
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Stratus
Figure 7.23
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Nimbostratus
Figure 7.23
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Stratocumulus
Figure 7.23
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Cumulus
Figure 7.23
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Cumulonimbus
Figure 7.23
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Cumulonimbus Development
Figure 7.24
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Fog  

• Fog a cloud layer at or very close to the
  surface formed when surface air temperatures and
  dewpt temperature are nearly identical
• Advection fog warm, moist air layers moves over
  a cold surface
• Evaporation fog dole air moves over warmer
  water body
• Radiation fog loss of longwave radiation over
  moist surface

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Advection Fog
When warm, moist air moves over cooler body of
water, what happens?
Figure 7.25
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Evaporation Fog
Cold air lies over warmer body of water, and
evaporation from water surface causes saturation
and fog. Also, sea smoke hazard.
Figure 7.26
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Radiation Fog
Loss of longwave radiation at night over moist
surface causes saturation.
Figure 7.28