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Title: Chapter 7 Water and Atmospheric Moisture


1
Chapter 7Water and Atmospheric Moisture
  • Geosystems 6e
  • An Introduction to Physical Geography

Robert W. Christopherson Charles E. Thomsen
2
Water and Atmospheric Moisture
  • TOPICS
  • Water on Earth
  • Unique Properties of Water  
  • Humidity  

3
Water on Earth  
  • Earths water originated from
  • Icy comets
  • Hydrogen and oxygen
  • Outgassing
  • Example geysers 
  • Eustasy, Glacio-eustasy, Isostasy

4
Distribution of Earths water todayLand and
Water Hemispheres
Figure 7.2
5
Ocean and Freshwater Distribution
Figure 7.3
6
Unique Properties of Water  
  • The water molecule H2O
  • Polarity to and to
  • hydrogen bonding
  • Surface tension
  • Capillarity

7
Unique Properties of Water  
  • Heat properties
  • Change of state requires energy be absorbed or
    released!
  • Phase changes
  • Freezing/melting (solid to liquid to solid)
  • Condensation/vaporization (gas to liquid to gas)
  • Sublimation/deposition (gas to solid to gas)

8
Evaporation Condensation
  • The process by which molecules break free of a
    liquid volume is evaporation
  • When water vapor molecules randomly collide with
    the water surface and bond with adjacent
    molecules is condensation

9
Three States of Water
Figure 7.5
10
(No Transcript)
11
Humidity
  • Humidity refers to water vapor in the air
  • Relative Humidity is the ratio (expressed as )
    of the amount of water vapor that is actually in
    the air compared to the maximum water vapor
    possible in the air at a given temperature
  • Air becomes saturated when the rate of
    evaporation and the rate of condensation reach
    equilibrium 100 relative humidity

12
Humidity
  • Equation for Relative Humidity 
  • actual water vapor
  • (specific humidity)
  • RH ------------------------------ X 100
    max amount that can be
    held at that temp
  • (saturation specific humidity)

13
Relative Humidity
Actualwater vapor
Figure 7.8
14
Relative Humidity
  • Relative humidity is the indication of how close
    the air is to saturation and when condensation
    will begin
  • Dew-point temperature not really a temperature,
    but a measure of moisture content
  • When air temperature tries to decrease below the
    dew point, surplus water vapor is removed from
    the air by condensation

15
Dew Point Temperature
16
Water Vapor in the Atmosphere
Figure 7.10
17
Distribution of Water Vapor
January
18
Distribution of Water Vapor
July
19
Humidity Patterns
Figure 7.11
20
Vapor Pressure
  • One of 2 measures of relative humidity
  • As water molecules evaporate and become part of
    the air, they become water-vapor molecules. In
    this state, they exert a portion of the air
    pressure called vapor pressure
  • Saturation vapor pressure
  • Increasing temperature means an increase in
    saturation vapor pressure kinetic energy

21
Specific Humidity
  • One of 2 measures of relative humidity
  • Specific humidity is a measure of humidity that
    remains constant as temperature and pressure
    change
  • Specific humidity is the mass of water vapor (g)
    per mass of air (kg) at any specified temperature

22
Condensation Nuclei
  • Pure water droplets are uncommon
  • Homogeneous nucleation
  • Hygroscopic aerosols
  • Dust, salt, pollution, ash
  • Heterogeneous nucleation

23
Humidity Instruments
Figure 7.14
24
Sling Psychrometer
  • Dry bulb thermometer measures normal air
    temperature
  • Wet bulb thermometer measures wet bulb depression

25
Potential Test Question
  • Relative humidity has an inverse
  • relationship with
  • A) dew-point temperature
  • B) air temperature
  • C) air pressure
  • D) eustasy

26
Potential Test Question
  • Define outgassing and use the term to explain the
    formation of the oceans on Earth.
  • Outgassing is the continuing process of water and
    water vapor emerging from layers deep below
    Earths crust. Billions of years ago, Earths
    surface cooled enough to hold water bodies. In
    this early atmosphere, outgassing occurred at a
    higher rate. Water vapor condensed and fell as
    torrential rains filling the lowest points on
    Earth with water. The oceans were formed in this
    way.

27
Potential Test Question
  • Which of the following has the highest water
    vapor content in the air?
  • A) southern Alabama
  • B) Oklahoma
  • C) eastern Montana
  • D) southern Missouri
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