Chapter 7 Water and Atmospheric Moisture Geosystems 6e An Introduction to Physical Geography Robert...
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Transcript of Chapter 7 Water and Atmospheric Moisture Geosystems 6e An Introduction to Physical Geography Robert...
Chapter 7Water and Atmospheric
Moisture
Geosystems 6eAn Introduction to Physical Geography
Robert W. ChristophersonCharles E. Thomsen
Water and Atmospheric Moisture
TOPICS:Adiabatic Processes
Atmospheric Stability
Clouds
Fog
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.
Buoyancy
Figure 7.15
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.
Adiabatic Processes
Figure 7.17
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
AtmosphericStability
Figure 7.20
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?
Examples of Stability
Figure 7.20
Unstable AtmosphereParcel of air is encouraged to rise
Examples of Stability
Figure 7.20
Stable AtmosphereParcel of air is discouraged from rising
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
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
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!
Atmospheric Temperatures and Stability
Figure 7.19
ELR ELR
Moisture Droplets
Figure 7.20
Raindrop and Snowflake Formation
Figure 7.22
Collision-coalescence process
Bergeron process
Cloud Types and Identification
Figure 7.23
12
3
5
6 7
8
9
104
2
Cirrus
Figure 7.23
Cirrostratus
Figure 7.23
Cirrocumulus
Figure 7.23
Altocumulus
Altostratus
Stratus
Figure 7.23
Nimbostratus
Figure 7.23
Stratocumulus
Figure 7.23
Cumulus
Figure 7.23
Cumulonimbus
Figure 7.23
Cumulonimbus Development
Figure 7.24
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
Advection Fog
Figure 7.25
When warm, moist air moves over cooler body of water, what happens?
Evaporation Fog
Figure 7.26
Cold air lies over warmer body of water, and evaporation from water surface causes saturation and fog. Also, sea smoke = hazard.
Figure 7.28
Radiation FogLoss of longwave radiation at night over moist surface causes saturation.