Chapter 7 Water and Atmospheric Moisture

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

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

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

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.

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

Atmospheric Stability
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

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

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

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
ELR ELR Figure 7.19

Moisture Droplets Figure 7.20

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

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

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

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

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

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

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