Robert W. ChristophersonCharlie Thomsen

Chapter 7Water and

Atmospheric Moisture

Water on the earth: Land and Water Hemispheres

Figure 7.2

•2/3 earth’s surface areas are water body•Most land is over northern Hemisphere

Ocean and Freshwater Distribution

Figure 7.3

Unique Properties of Water  Heat properties 

Phase change

Latent heat: heat related to water phase change

Heat properties of water in nature  

Three States of Water

Figure 7.5

Phase Changes

Figure 7.7

Uniqueness of Ice Forms

Figure 7.6

HumiditySaturation: air is holding the maximum

amount vapor at the given air temperature.

Expressions of humidity  Vapor pressure

Specific humidity

Relative humidity

Dew point

Instruments

Water Vapor in the Atmosphere

Figure 7.10

Water Vapor in the Atmosphere

Figure 7.10

Vapor pressure: pressure created by water vapor alone

Saturation Vapor Pressure:maximum vapor pressure at a given air temperature.It increases with air temperature, more rapidly at higher air temperatures

Figure 7.12

Specific humidity: the amount of water (g) vapor in a kg of dry air

Maximum Specific Humidity: the saturation specific humidity at a given air temperature

Figure 7.13

Relative Humidity: (actual vapor)/(saturation vapor); how close the

atmosphere to the saturation

Figure 7.8

Humidity Patterns

Air temperature increases, the relative humidity decreases if there is no change in vapor amount in the air

Humidity Instruments: hair hygrometer; dry-and-wet bulb

thermometer

Figure 7.14

Dew point temperatureThe air temperature when air reaches

saturation (when dew starts to form)

Clouds and FogCloud Formation Processes  

Cloud Types and Identification  

Fog  

Cloud Formation Processes

Moisture droplets

Cloud-condensation nuclei

Moisture Droplets

Figure 7.20

Raindrop and Snowflake Formation

Figure 7.21

Collision and coalescence: large droplets merges with smaller ones

Ice crystal process: ice crystals grow and water droplets evaporate

Cloud Types and Identification  

Figure 7.22

High clouds: cirrus, cirrostratus, cirrocumulusMiddle clouds: altostratus, altocumulusLow clouds: stratus, stratocumulus, nimbostratus

Clouds with vertical development:Cumuluscumulonimbus

Cirrus

Figure 7.22

Cirrostratus

Figure 7.22

Altocumulus

Figure 7.22

Altostratus

Figure 7.22

Nimbostratus

Figure 7.22

Stratus

Figure 7.22

Cumulus

Figure 7.22

Cumulonimbus

Figure 7.22

Cumulonimbus Development

Figure 7.23

Thunderstorm cloud: with updraft and downdraft in different parts of the cloud

Fog: clouds with based on the ground  

Advection fog

Evaporation fog

Upslope fog

Valley fog

Radiation fog

Advection Fog: warm and moist air moves over a cooler surface

Figure 7.24

Evaporation Fog: warm water evaporates into colder air above

Figure 7.25

Radiation Fog: radiation cooling of the land surface chills the near surface air.Condition: clear sky, calm (light wind).Most common in fall and winter

Figure 7.27