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.