1. Chapter 7 Water and Atmospheric Moisture
Geosystems 6e
An Introduction to Physical Geography
Robert W. Christopherson
Charles E. Thomsen

2. Water and Atmospheric Moisture
TOPICS:
Adiabatic Processes
Atmospheric Stability 
Clouds 
Fog  

3. 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.

4. Buoyancy
Figure 7.15

5. 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.

6. Adiabatic Processes
Figure 7.17

7. 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

10. Atmospheric Stability
Figure 7.20

11. 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

12. Unstable Atmosphere Parcel of air is encouraged to rise
 Examples of Stability
 Unstable Atmosphere Parcel of air is encouraged to rise
Figure 7.20

13. Stable Atmosphere Parcel of air is discouraged from rising
 Examples of Stability
 Stable Atmosphere Parcel of air is discouraged from rising
Figure 7.20

14. Atmospheric Stability
To determine atmospheric stability:
Compare the ELR with the DAR (or DALR) and MAR (or WALR)
If ELR < MAR < DAR = STABLE
If ELR > DAR > MAR = UNSTABLE
If MAR < ELR < DAR = CONDITIONALLY UNSTABLE

15. 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) > DAR (10) > MAR (6) then?
If ELR > DAR > MAR = UNSTABLE

16. 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!

17. Atmospheric Temperatures and Stability
ELR
ELR
Figure 7.19

18. Moisture Droplets
Figure 7.20

19. Raindrop and Snowflake Formation
Bergeron process
Collision-coalescence process
Figure 7.22

20. Cloud Types and Identification 1 2 3 5 6 7 8 9 10 4
Figure 7.23

21. Cirrus
Figure 7.23

22. Cirrostratus
Figure 7.23

23. Cirrocumulus
Figure 7.23

24. Altocumulus

25. Altostratus

26. Stratus
Figure 7.23

27. Nimbostratus
Figure 7.23

28. Stratocumulus
Figure 7.23

29. Cumulus
Figure 7.23

30. Cumulonimbus
Figure 7.23

31. Cumulonimbus Development
Figure 7.24

32. 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

33. When warm, moist air moves over cooler body of water, what happens?
Advection Fog
When warm, moist air moves over cooler body of water, what happens?
Figure 7.25

34. 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

35. Radiation Fog
Loss of longwave radiation at night over moist surface causes saturation.
Figure 7.28