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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   Atmospheric Stability   Clouds and Fog  .

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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   • Atmospheric Stability   • Clouds and Fog  

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

  4. Ocean and Freshwater Distribution Figure 7.3

  5. Unique Properties of Water   • The water molecule: H2O • Polarity: + to – and – to + • = hydrogen bonding • Surface tension • Capillarity

  6. 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)

  7. 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

  8. Three States of Water Figure 7.5

  9. 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

  10. 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)

  11. Cooling Warming Relative Humidity Actualwater vapor Figure 7.8

  12. 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

  13. Dew Point Temperature

  14. Distribution of Water Vapor January

  15. Distribution of Water Vapor July

  16. Humidity Patterns Figure 7.11

  17. 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

  18. 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 • Maximum specific humidity

  19. Condensation Nuclei • Pure water droplets are uncommon • Homogeneous nucleation • Hygroscopic aerosols • Heterogeneous nucleation • Condensation nuclei

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

  21. 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

  22. Adiabatic Processes   • Adiabatic processes • Begins with a parcel of air • 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.

  23. Adiabatic Processes   • Adiabatic processes • Ascending or descending air will undergo changes in temperature with no exchange of heat. This is an adiabatic process. • Changes in temperature will be due solely to changes in pressure! (Example?) • Note difference with parcel of air undergoing changes in temperature when we discussed humidity! No motion was implied! • Heat WAS exchanged = diabatic process.

  24. Adiabatic processes Note also differences in the volumes of the parcels of air between diabatic (heat exchange) and adiabatic (no-heat exchange): Cooling Diabatic Process Adiabatic Processes  

  25. Adiabatic Process!

  26. Buoyancy Figure 7.15

  27. Adiabatic Processes Figure 7.17

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