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Chapter 7 Water and Atmospheric Moisture

Chapter 7 Water and Atmospheric Moisture. Geosystems 6e An Introduction to Physical Geography. Robert W. Christopherson Charles E. Thomsen. Water and Atmospheric Moisture. TOPICS: Water on Earth Unique Properties of Water   Humidity  . Water on Earth  . Earth’s water originated from

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Chapter 7 Water and Atmospheric Moisture

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  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   • Earth’s water originated from • Icy comets • Hydrogen and oxygen • Outgassing • Example: geysers  • Eustasy, Glacio-eustasy, Isostasy

  4. Distribution of Earth’s 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. 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

  11. 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)

  12. Cooling Warming Relative Humidity Actualwater vapor Figure 7.8

  13. 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

  14. Dew Point Temperature

  15. Water Vapor in the Atmosphere Figure 7.10

  16. Distribution of Water Vapor January

  17. Distribution of Water Vapor July

  18. Humidity Patterns Figure 7.11

  19. 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

  20. 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

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

  22. Humidity Instruments Figure 7.14

  23. Sling Psychrometer • Dry bulb thermometer: measures normal air temperature • Wet bulb thermometer: measures wet bulb depression

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

  25. 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 Earth’s crust. Billions of years ago, Earth’s 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.

  26. 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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