Ch.18 Notes Mc Neely 2009


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Ch.18 Notes Mc Neely 2009

  1. 1. Moisture, Clouds, & Precipitation Ch. 18 Earth-Space Science Bremen High School Teacher : Aaron McNeely
  2. 2. Water in the Atmosphere Sec 18.1 <ul><li>Water vapor </li></ul><ul><ul><li>Water in a gas form </li></ul></ul><ul><ul><li>The source of all clouds, condensation, and precipitation </li></ul></ul><ul><ul><li>For weather, water vapor is the most important gas in the atmosphere </li></ul></ul><ul><li>Precipitation is any water, solid or liquid, that falls from the sky </li></ul><ul><li>Water vapor is 0-4% of atmospheric gases </li></ul>
  3. 3. Water’s Changes of State <ul><li>Three states of matter: </li></ul><ul><ul><li>Solid, liquid, and gas </li></ul></ul><ul><li>Water can change between these states in earth’s atmosphere, termed the water cycle </li></ul>
  4. 4. Water Cycle <ul><li>Water constantly moves among the oceans, fresh water bodies, and atmosphere </li></ul><ul><li>Planet-wide phenomena powered by the sun </li></ul>
  5. 5. Steps in the Water Cycle <ul><li>General Steps : </li></ul><ul><ul><li>Water evaporates from the ocean </li></ul></ul><ul><ul><li>Water falls as precipitation upon land or ocean (cycle complete) </li></ul></ul><ul><ul><li>Water that falls on land becomes run-off or soaks into the ground (infiltration) </li></ul></ul><ul><ul><li>Run-off carries water directly back to the ocean in streams and rivers </li></ul></ul><ul><ul><li>Groundwater eventually joins lakes and rivers </li></ul></ul><ul><ul><li>Plants absorb water and release it back into the atmosphere (transpiration) </li></ul></ul><ul><ul><li>Cycle complete when land-based water reaches the ocean </li></ul></ul>
  6. 6. Phenomena of the Water Cycle <ul><li>Evaporation </li></ul><ul><li>Precipitation </li></ul><ul><li>Infiltration </li></ul><ul><li>Run-off </li></ul><ul><li>Transpiration </li></ul>
  7. 7. Water Cycle
  8. 8. Water’s Changes of State <ul><li>Evaporation—Liquid to gas </li></ul><ul><li>Condensation—Gas to liquid </li></ul><ul><li>Melting—Solid to liquid </li></ul><ul><li>Freezing—Liquid to solid </li></ul><ul><li>Sublimation—Solid to gas </li></ul><ul><li>Deposition—Gas to solid </li></ul>
  9. 9. Evaporation <ul><li>Liquid to a gas </li></ul><ul><li>Energy required, termed latent heat </li></ul><ul><li>Evaporation is a cooling process, removes heat from surroundings </li></ul>
  10. 10. Condensation <ul><li>Gas to liquid </li></ul><ul><li>Latent heat is released </li></ul><ul><li>Ex: Cold beverage, morning car </li></ul>
  11. 11. Melting <ul><li>Solid to liquid </li></ul><ul><li>Heat required, used to break bonds between water molecules </li></ul><ul><li>Latent heat is the energy source for weather such as thunderstorms, tornadoes, and hurricanes </li></ul>
  12. 12. Freezing <ul><li>Liquid to solid </li></ul><ul><li>Water releases latent heat during freezing </li></ul><ul><li>Molecules in water become trapped in the crystal structure of ice </li></ul>                                                  
  13. 13. Sublimation <ul><li>Solid to gas, skips liquid phase </li></ul><ul><li>Dry ice (frozen carbon dioxide) sublimates, also freezer ice cubes can shrink </li></ul>Dry ice
  14. 14. Deposition <ul><li>Gas to a solid, opposite of sublimation </li></ul><ul><li>Frost </li></ul>
  15. 15. Water’s Changes of State Diagram <ul><li>Red arrows = absorption of latent heat </li></ul><ul><li>Blue arrows = release of latent heat </li></ul>
  16. 16. Humidity <ul><li>Water vapor in the air </li></ul><ul><li>Saturation occurs when air holds all the water vapor that it is able to hold (at a particular temperature and pressure) </li></ul><ul><li>Saturated warm air holds more water than cool saturated air </li></ul>
  17. 17. Relative Humidity <ul><li>A ratio of the air’s water vapor content compared to the amount it could possibly hold </li></ul><ul><li>Expressed as a percent </li></ul><ul><li>100% is saturated air </li></ul>
  18. 18. Changes in Relative Humidity <ul><li>When the amount of water vapor in the air is constant: </li></ul><ul><ul><li>Lowering temperature increases relative humidity </li></ul></ul><ul><ul><li>Raising temperature decreases relative humidity </li></ul></ul>
  19. 19. Relative Humidity Example <ul><li>Amount air can possibly hold </li></ul><ul><li>Assume no water is taken or added from the parcel of air </li></ul><ul><li>Relative humidity increases just by lowering temperature </li></ul>Relative humidity = 7g/7g = 100% Relative Humidity = 7g/14g = 50% Actual water vapor = 7g Actual water vapor = 7g Saturation = 7g water vapor Saturation = 14g water vapor Temperature = 10 ° C Temperature = 20 ° C
  20. 20. Dew Point <ul><li>A measure of humidity </li></ul><ul><li>Dew point is the temperature at which a quantity of air becomes saturated </li></ul><ul><li>Below dew point, the air’s excess water vapor condenses as dew, fog, or clouds </li></ul><ul><li>High dew points indicate moist air, low dew points indicate dry air (warm air holds more moisture, etc.) </li></ul>
  21. 21. Dew on a Spider Web
  22. 22. Water Vapor for Saturation Data : Table 1 on p. 506, Prentice Hall Earth Science
  23. 23. Sling Psychrometer Wet bulb <ul><li>Device to measure relative humidity, uses two thermometers and wet and dry bulbs </li></ul>
  24. 24. Adiabatic Temperature Changes (Sec 18.2) <ul><li>Adiabatic heating or cooling </li></ul><ul><ul><li>Compressing or expanding air changes temperature </li></ul></ul><ul><ul><li>Compressed air is warmer ,expanded air is cooler </li></ul></ul><ul><ul><li>No heat is added or removed </li></ul></ul>
  25. 25. Adiabatic Cooling <ul><li>Rising air cools due to decrease in pressure </li></ul><ul><li>This adiabatic cooling causes clouds to form </li></ul>
  26. 26. Dry & Wet Adiabatic Rates <ul><li>Rising air cools 10°C every 1000 meters, termed dry adiabatic cooling rate </li></ul><ul><li>After saturation, clouds form, cooling rate drops, termed wet adiabatic (5°C for every 1000 meters) </li></ul>
  27. 27. Wet & Dry Adiabatic Lapse Rates
  28. 28. Cloud Formation by Adiabatic Cooling Cooling = 10 ° C per 1000 m Cooling = 5 ° C per 1000 m
  29. 29. Processes That Lift Air (for cloud creation) <ul><li>Orographic lifting </li></ul><ul><li>Frontal wedging </li></ul><ul><li>Convergence </li></ul><ul><li>Local convection </li></ul>
  30. 30. Orographic Lifting <ul><li>When air is forced up the sides of mountains </li></ul><ul><li>As the air rises, adiabatic cooling causes cloud formation and precipitation </li></ul><ul><li>Earth’s rainiest locations are often on the windward sides of mountain ranges </li></ul><ul><li>Leeward side of mountain range results in rain shadow desert </li></ul>
  31. 31. Orographic Processes Windward side Leeward side
  32. 32. Orographic Clouds Where is the air rising?
  33. 33. Take me to your leader.
  34. 35. Frontal Wedging <ul><li>Warm and cold air masses collide (fronts) </li></ul><ul><li>Warm air is forced up over the cooler air </li></ul><ul><li>Rising air cools adiabatically creating clouds, precipitation, and storms </li></ul>
  35. 36. Frontal Wedging and Clouds
  36. 37. Convergence <ul><li>Occurs when air comes together after moving from different directions </li></ul><ul><li>Air rises at the collision and cools adiabatically creating clouds and storms </li></ul>
  37. 38. Convergence and Clouds Convergence often creates storms in Florida
  38. 39. Local Convection <ul><li>Differences in reflectivity, e.g., asphalt road versus grassy field create areas of warmer and cooler air </li></ul><ul><li>Rising warm air creates clouds </li></ul><ul><li>Sinking cool air is clear </li></ul><ul><li>Rising air also referred to as thermals </li></ul><ul><li>Thermals affect birds and airplanes </li></ul>
  39. 40. Localized Convection
  40. 41. Birds and Thermals Birds, like this condor, often sail using thermals
  41. 42. Convective Cells <ul><li>Convection cells often develop in stable air creating lumpy clouds (cumulus) separated by clear areas </li></ul>
  42. 43. Fair Weather Cumulus Where is air rising and sinking?
  43. 44. Stability <ul><li>Temperature inversions, air overhead is warmer, creates stability </li></ul><ul><li>Warmer air acts as a cap over the cooler air </li></ul><ul><li>Surface air can become stagnant and polluted, dangerous air </li></ul>
  44. 45. Condensation Nuclei <ul><li>Condensation nuclei are small particles around which water can start to condense </li></ul><ul><li>Needed for cloud formation </li></ul><ul><li>Microscopic dust, smoke, ocean salt, meteoritic material (space) </li></ul>
  45. 46. Tiny Particles
  46. 47. Clouds Sec 18.3 <ul><li>Visible masses of tiny water droplets or ice crystals suspended in the atmosphere </li></ul><ul><li>Latin names </li></ul><ul><li>Classified according to form (shape) and height </li></ul>
  47. 48. Form and Height <ul><li>Three Forms: </li></ul><ul><ul><li>Cirrus </li></ul></ul><ul><ul><li>Cumulus </li></ul></ul><ul><ul><li>Stratus </li></ul></ul><ul><li>Heights: </li></ul><ul><ul><li>Low </li></ul></ul><ul><ul><li>Middle (alto) </li></ul></ul><ul><ul><li>High </li></ul></ul>
  48. 49. Cirrus <ul><li>Latin for “curl of hair” </li></ul><ul><li>High, white, and thin, resemble feathers or cotton candy </li></ul><ul><li>Ice crystals </li></ul>
  49. 50. Cirrus Clouds Cirrus clouds are high, white, and thin
  50. 51. Cumulus <ul><li>Latin for “a pile” </li></ul><ul><li>Rounded, lumpy cloud masses, resemble cauliflower </li></ul><ul><li>Normally a flat base and lumpy top </li></ul><ul><li>Water droplets </li></ul>
  51. 52. Cumulus Clouds Cumulus clouds are lumpy
  52. 53. Stratus <ul><li>Latin for “a layer” </li></ul><ul><li>Flat, layered, sheet-like clouds </li></ul><ul><li>Extensive, create gray, dismal conditions </li></ul><ul><li>Low stratus clouds - water droplets </li></ul><ul><li>High stratus clouds - ice crystals </li></ul><ul><li>Often create halos around the sun or moon </li></ul>
  53. 54. Stratus Clouds (flat) Stratus clouds form flat layers
  54. 55. High Clouds <ul><li>Usually composed of ice crystals </li></ul><ul><ul><li>Examples : </li></ul></ul><ul><ul><ul><li>Cirrus </li></ul></ul></ul><ul><ul><ul><li>Cirrostratus </li></ul></ul></ul><ul><ul><ul><li>Cirrocumulus </li></ul></ul></ul>
  55. 56. Cirrostratus These clouds produced a halo around the sun
  56. 57. Middle Clouds <ul><li>Middle clouds have the prefix alto in their names </li></ul><ul><ul><li>Examples : </li></ul></ul><ul><ul><ul><li>Altostratus </li></ul></ul></ul><ul><ul><ul><li>Altocumulus, </li></ul></ul></ul>
  57. 58. Altocumulus (middle-height, lumpy)
  58. 59. Altostratus (middle, flat)
  59. 60. Low Clouds <ul><li>Low clouds produce local weather such as rain </li></ul><ul><li>Prefix nimbo indicates rain </li></ul><ul><ul><li>Examples : </li></ul></ul><ul><ul><ul><li>Stratus </li></ul></ul></ul><ul><ul><ul><li>Stratocumulus </li></ul></ul></ul><ul><ul><ul><li>Nimbostratus </li></ul></ul></ul>
  60. 61. Nimbostratus (rainy, low)
  61. 62. Vertical Clouds <ul><li>Vertical clouds extend through all of these height levels </li></ul><ul><ul><li>Example : </li></ul></ul><ul><ul><ul><li>Cumulonimbus </li></ul></ul></ul>
  62. 63. Cumulonimbus (vertical) Cumulonimbus clouds often create powerful storms
  63. 64. Cloud Classification
  64. 65. Cloud Summary Table C u m u l o n I m b u s Cumulus Stratocumulus Stratus Nimbostratus Fog Low Altocumulus Altostratus Middle Cirrocumulus Cirrostratus Cirrus High
  65. 66. Fog <ul><li>When a cloud develops at ground level </li></ul><ul><li>Results when the ground cools below dew point </li></ul><ul><li>Fog condenses in low areas </li></ul><ul><li>Also can form by evaporation when cool air moves over a warmer body of water </li></ul>
  66. 67. Fog in San Francisco
  67. 68. Mechanisms of Precipitation <ul><li>Tiny droplets of airborne moisture collect into larger masses </li></ul><ul><li>A one million times change in volume </li></ul><ul><li>Two processes: </li></ul><ul><ul><li>Bergeron process </li></ul></ul><ul><ul><li>Collision-coalescence process </li></ul></ul>
  68. 69. Bergeron Process <ul><li>Cold clouds </li></ul><ul><li>Supercooled droplets form ice crystals </li></ul><ul><li>Fall as precipitation </li></ul><ul><li>Supercooling occurs when droplets of water remain in a liquid state even below the normal freezing temperature (0C) </li></ul>
  69. 70. Bergeron Process Diagram <ul><li>Ice crystal grow at the expense of cloud droplets </li></ul><ul><li>Eventually the ice crystal becomes large enough to fall as precipitaiton (snow) </li></ul>
  70. 71. Collision-Coalescence Process <ul><li>Warm clouds </li></ul><ul><li>Condensation nuclei collect tiny droplets of vapor </li></ul><ul><li>Droplets succumb to gravity and fall as precipitation </li></ul>
  71. 72. Forms of Precipitation <ul><li>Function of temperature in lower atmosphere </li></ul><ul><li>Forms of Precipitation: </li></ul><ul><ul><li>Rain, Snow, Sleet, Glaze, Hail </li></ul></ul>
  72. 73. Rain and Snow <ul><li>Rain is drops of water at least 0.5mm in diameter </li></ul><ul><li>Snow (ice crystals) will survive on the ground if surface temp is below 39 ° F (4 ° C) </li></ul><ul><li>Snow can range from tiny crystals to large, fluffy clumps </li></ul>
  73. 74. Sleet & Glaze <ul><li>Sleet : Small particles of clear ice, fleet forms when tiny water droplets descend through a colder air layer above the earth’s surface </li></ul><ul><li>Glaze : Fall of supercooled water droplets, can create clear ice coating on surface objects (ice storms) </li></ul>
  74. 75. Ice Storms Ice storms can result in power outages
  75. 76. Hail <ul><li>Solid lumps of ice produced in cumulonimbus clouds </li></ul><ul><li>In these clouds, solid particles of ice move vertically and grow by collectiing supercooled droplets </li></ul><ul><li>Onion-like internal layers </li></ul><ul><li>5-140mm in size </li></ul>
  76. 77. Hailstones
  77. 78. Hail Damage
  78. 79. Acid Rain <ul><li>Precipitation that forms in clouds containing air pollution </li></ul><ul><li>Pollution particles act as condensation nuclei </li></ul><ul><li>Acid rain can damage forests and stone structures </li></ul>
  79. 80. Acid Rain and Stonework 1908 1968