Chapter 6: Moisture, Condensation, and Precipitation

Physical Physical GeographyGeographyNinth EditionNinth Edition

Robert E. Gabler

James. F. Petersen

L. Michael Trapasso

Dorothy Sack

Ch. 6: Moisture, Condensation, and Precipitation

Hydrosphere

• Hydrosphere: liquid river, lakes, oceans, rain, ice water droplets, and water vapor.

• If the ice floating in a beverage glass melts completely before you can drink it, will the liquid rise, fall, or remain the same?

6.1 Hydrologic Cycle

• Hydrologic cycle: circulation of water over earth. A closed system.

• Can you distinguish between the snow on the land, Greenland's ice sheet, and the seasonal pack ice?

6.1 Hydrologic Cycle

• Earth’s Water Resources• How might global warming or cooling alter the image below?

6.1 Hydrologic Cycle

• Hydrologic system– Water changes of state– Redistribution of energy

6.2 Water in the Atmosphere

• Water Budget and Heat Budget– Water vapor absorbs and reflects energy– Water Budget: Total quantity of water remains

the same. Any deficit must balance gains. • Latent Heat• Heat transfer involved with evaporation and

condensation is huge! • The energy stored and transferred in phase

changes provides the power for Earth’s storms!

• Saturation: air at a certain temperature holds all of the water vapor possible. It has reached capacity.

• Dew Point: the temperature at which the air becomes saturated. The dew point is changes.

6.2 Water in the Atmosphere

• Humidity: Amount of water vapor in the air.

• 3 different ways to measure Humidity:– Absolute Humidity– Specific Humidity– Relative Humidity (R.H.)

6.2 Water in the Atmosphere

• What do you notice about the relationship between these two lines?

6.2 Water in the Atmosphere

• Evapotranspiration: Plants giving up water.• Rate of Evaporation• Potential Evapotranspiration

6.3 Sources of Atmospheric Moisture

• Distribution of Actual Mean Evapotranspiration

6.3 Sources of Atmospheric Moisture

• Water Budget System– When would irrigation at this site be necessary?

6.3 Sources of Atmospheric Moisture

• Condensation: occurs air is saturated to the dew point. The R.H. becomes 100%.

• Condensation requires the presence of Condensation Nuclei. These provide a surface for the water vapor to condense on.

• Fog and Clouds form when water vapor condenses and a large number of these droplets form a mass.

6.4 Condensation

• Dew: condensation of water vapor at or near Earth’s surface

• White frost

• Rime

6.4 Condensation

• Clouds: source of all precipitation

• Cloud forms:– Strato (low)– Alto (middle)– Cirro (high)

6.4 Condensation

• Cirrus• Stratus• Cumulus• Stratocumulus• Nimbus: rain

falling• Nimbostratus• Cumulonimbus

6.4 Condensation

• Fog is a cloud at the ground surface.

• Types of Fog:– Radiation Fog– Advection Fog– Upslope Fog

6.4 Condensation

• Adiabatic heating: descending air is compressed by increasing pressure and thus warms at 5.6oF/1000 feet (10oC/1000 meters)

• Adiabatic cooling: rising parcel of air cools as with decreasing pressure. It cools at the same rate as above.

6.4 Condensation

• Dry adiabatic lapse rate– Cooling of a parcel

before condensing– 5.6oF/1000 feet

(10oC/1000 meters)

• Wet adiabatic lapse rate – Cooling of a parcel after

condensing– 3.2oF/1000 feet

(5oC/1000 meters

6.4 Condensation

• The wet and dry adiabatic rate is NOT the same as the normal lapse rate (environmental lapse rate).

6.4 Condensation

• Stability: environment lapse rate < dry adiabatic • Instability (unstable): environment lapse rate > dry adiabatic

6.4 Condensation

• Relative sizes of:– Raindrops– cloud droplets– condensation nuclei

Q: If the diameter of a raindrop is 100 times larger than a cloud droplet, why does it take a million droplets to produce one raindrop?

6.5 Precipitation Processes

• The wet and dry adiabatic rate is NOT the same as the normal lapse rate (environmental lapse rate).

6.5 Precipitation Processes

• Cloud droplet formation process– Collision-coalescence

(warm clouds)– Bergeron (ice crystal)

process• Cold cloud• Supercooled water

6.5 Precipitation Processes

• Q: What is the difference between water and supercooled water?

6.5 Precipitation Processes

• Major forms of Precipitation– Rain– Drizzle– Snow– Sleet– Hail– Freezing rain

6.5 Precipitation Processes

• Factors necessary for precipitation– Moist air– Condensation nuclei– Uplift mechanism

(rising air)

6.5 Precipitation Processes

• Uplift mechanisms– Convectional– Frontal– Cyclonic (convergence)– Orographic

6.5 Precipitation Processes

• Convectional– Hot air rises– Cooler air sinks– Most common humid

equatorial and tropics– In which case, will

clouds appear due to convectional lifting?

6.5 Precipitation Processes

• Frontal: Boundary zone between relatively warm and cold air

• Cyclonic– also known as convergence– Air moves counterclockwise towards the

center of a low pressure.

6.5 Precipitation Processes

• Orographic– air forces upward

due to land barriers (mountains, plateaus)

– Rain shadow occurs on the leeward side

– windward

6.5 Precipitation Processes

What kind of air movement is common to all four diagrams?

6.5 Precipitation Processes

• Distribution of Precipitation– # of raindays (0.01

inches of rain or more)

– Average monthly precipitation

Q: How would this rainfall pattern affect agriculture?

6.5 Precipitation Processes

• Horizontal Distribution of Precipitation– 4 Lifting mechanisms– Temperature (warmer

air holds more water)– General atmospheric

circulation– Latitude zones– Windward side– Land masses

6.5 Precipitation Processes

In general, where on Earth’s surface does the heaviest rain fall?

Q: Compare this figure with 5.11. What is the relationship between world rainfall patterns and pressure distribution?

6.5 Precipitation Processes

Q: Compare this figure with 6.23 (World average annual precipitation). What are some of the similarities and differences?

6.6 Variability of Precipitation

Physical Geography

End of Chapter 6: Moisture, Condensation, and Precipitation