Clouds and fog

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Naval Science II
Naval Sciences
Meteorology

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Clouds and fog

  1. 1. CHAPTER 2 CLOUDS AND FOG
  2. 2. Tiny particles of dust, pollen from plants, factory smoke, and salt particles from oceans are always present in the air. These fragments are called hygroscopic nuclei.
  3. 3. Tiny particles that absorb or attract moisture from the air Hygroscopic Nuclei
  4. 4. Clouds form when: • Water vapor rises • Vapor condenses • Droplets cling to hygroscopic nuclei • Nuclei bunch together and form clouds or fog
  5. 5. Three things may happen to the water droplets: • Reevaporate and rise • Rise and freeze into ice crystals • Collide with other nuclei and form larger drops
  6. 6. Cloud formations give clues concerning the forces at work in our atmosphere.
  7. 7. Fragments of matter that are always in the air are called _________ nuclei. a. hydroscopic b. hygroscopic c. psychroscopic d. psychrodropic
  8. 8. Cirrus Stratus Cumulus There are three basic cloud types.
  9. 9. A cloud of a class characterized by thin white filaments or narrow bands and a composition of ice crystals: of high altitude, about 20,000 - 40,000 feet Cirrus
  10. 10. A cloud of a class characterized by dense individual elements in the form of puffs, mounds, or towers, with flat bases and tops that often resemble cauliflower Cumulus
  11. 11. A cloud of a class characterized by a gray, horizontal layer with a uniform base, found at a lower altitude than altostratus, usually below 8,000 feet Stratus
  12. 12. There are also other types of clouds having names with combinations of the following: • Nimbus - rain • Alto - high • Fracto - fragmented or windblown
  13. 13. Clouds are sometimes classified by altitudes at which they most frequently occur: • Low - surface - 7,000 feet • Middle - 7,000 - 20,000 feet • High - above 20,000 feet • Towering - exceptionally high cloud with its base in low-altitude
  14. 14. There are ten general types of clouds grouped into low, middle, and high categories.
  15. 15. Low Clouds Stratus Nimbostratus Stratocumulus Cumulus Cumulonimbus
  16. 16. • Lowest cloud type • Gray layer with uniform base • May cause drizzle, but never rain • Fog becomes stratus when it lifts Stratus
  17. 17. • Dark, shapeless, rain-laden • Often have streaks of rain extending to ground • Often seen in summer at base of thunderheads • Brings steady, heavy snow in winter Nimbostratus
  18. 18. A cloud of a class characterized by a formless layer that is almost uniformly dark gray, a rain cloud of the larger type, of low altitude, usually below 8,000 feet Nimbostratus
  19. 19. Stratocumulus • Irregular, rounded masses spread out in puffy or rolling layers • Usually gray with darker spots • Do not produce rain • Usually precede bad weather
  20. 20. A cloud of a class characterized by large dark, rounded masses, usually in groups, lines, or waves, the individual elements being larger than those in altocumulus and the whole being at a lower altitude, usually below 8,000 feet Stratocumulus
  21. 21. Cumulus • Dense, puffy clouds with a beautiful, cauliflower-like appearance • They rise by day and disappear at night • Fleecy cumulus clouds usually mean fair weather ahead
  22. 22. • Dense clouds of the towering variety • The base is a dark nimbus rain cloud • May produce severe thunderstorms and tornadoes Cumulonimbus (Thunderheads)
  23. 23. A cloud of a class indicative of thunderstorm conditions, characterized by large, dense towers that may reach altitudes of 75,000 feet, uniform except for the tops, which appear fibrous because of the presence of ice crystals Cumulonimbus
  24. 24. The upper portion of a cumulus cloud characterized by dense, sharply defined cauliflower-like upper parts and sometimes of great verticality Thunderhead
  25. 25. Middle Clouds Altocumulus Altostratus
  26. 26. Altocumulus • Gray or whitish layers, puffy, fleecy • Made up of water droplets • Sometimes produce a pale blue or yellow corona • Presence means rain is probable within 24 hours
  27. 27. A cloud of a class characterized by globular masses or rolls in layers or patches, the individual elements being larger and darker than those of cirrocumulus and smaller than those of stratocumulus: of medium altitude, about 8,000 - 20,000 feet Altocumulus
  28. 28. Altostratus • Dense sheets of gray or blue • Sun or Moon will show through but without corona • Light rain is likely within 24 hours
  29. 29. A cloud of a class characterized by a generally uniform gray sheet or layer, lighter in color than nimbostratus and darker than cirrostratus: of medium altitude, about 8,000 - 20,000 feet Altostratus
  30. 30. High Clouds Cirrus Cirrostratus Cirrocumulus
  31. 31. Cirrus • Thin, wispy, made up of ice crystals • Called “mare’s tails” • If scattered, indicate clear, cold weather • If in parallel lines, indicate violent change in weather within 36 hours
  32. 32. Cirrostratus • May nearly cover the sky with a filmy cloud • Curly appearance at their edges • Form large halos around the Sun and Moon • Indicate clear and cold weather
  33. 33. A cloud of a class characterized by a composition of ice crystals and often by the production of halo phenomena and appearing as a whitish and usually somewhat fibrous veil, often covering the whole sky and sometimes so thin as to be hardly discernible: of high altitude, 20,000 - 40,000 feet Cirrostratus
  34. 34. Cirrocumulus • Thin, patchy clouds that sometimes form in wavelike patterns • Do not leave shadows • Precipitation usually follows within 24 hours
  35. 35. A cloud of a class characterized by thin, white patches, each of which is composed of very small granules or ripples: of high altitude, 20,000 - 40,000 feet Cirrocumulus
  36. 36. Clouds have been leading lost seamen, navigators, and explorers to land since the days of the earliest hardy sea voyagers.
  37. 37. Stationary clouds on the horizon usually indicate an island is close by.
  38. 38. In the tropics, clouds often reflect the colors of the sandy beaches or coral reefs below.
  39. 39. Precipitation (rain, snow, sleet, and hail) cannot occur without clouds.
  40. 40. Temperature and presence of hygroscopic nuclei or ice crystals determine if there will be precipitation and in what form it will take.
  41. 41. Raindrops form when moist air is cooled to the point where the moisture condenses into heavy drops.
  42. 42. Cloud moisture droplets are 1/2,500 of an inch in diameter. If the droplet grows to 1/125 of an inch, it will fall from the cloud. The combining of moisture droplets is called coalescence. Large Raindrop Small Raindrop Not to Scale
  43. 43. To grow together into one body Coalescence
  44. 44. Coalescence occurs in two known ways: • Bigger droplets move about slowly, bump into other droplets and combine with them (low clouds).
  45. 45. Coalescence occurs in two known ways: • Ice crystals and water droplets form near each other, the droplets evaporate and resulting vapor collides with ice crystals and condenses into snow or ice pellets. They melt into rain as they pass through warmer air at lower altitudes.
  46. 46. Rainmaking has been a concern of humans since the most ancient times.
  47. 47. Rain dances, sacrifices, drums, cannons, and smoke have all been used in an attempt to make rain, especially during a drought.
  48. 48. Seeding a large cumulus cloud with one pound of artificial nuclei made of dry-ice or silver-iodide crystals can start a shower.
  49. 49. Seeding can cause: • Rain to fall sooner • More rain to fall • Rain to fall from a cloud that normally would not produce rain
  50. 50. Seeding cannot cause: • Rain to fall from fair skies or fair-weather cumulus clouds • Rain to fall over a large area
  51. 51. Sleet occurs when rain formed in relatively warm air falls through a layer of freezing air.
  52. 52. Hail usually occurs in the summertime. It begins as raindrops, that updrafts take to greater heights. They are coated with water from lower clouds, lifted again and again until too heavy to be lifted.
  53. 53. Most hailstones are smaller than marbles. Hailstones as large as baseballs have killed people and animals.
  54. 54. In wintertime, when the upper air is very cold, water vapor will condense into ice crystals. Snow is the result.
  55. 55. Dew is water vapor that condenses on objects that have cooled below the condensation point of the air around them.
  56. 56. Frost is similar to dew, but it forms at temperatures below freezing.
  57. 57. A covering of minute ice needles, formed from the atmosphere at night upon the ground and other exposed objects when they have cooled by radiation below the dew point, and when the dew point is below the freezing point Frost
  58. 58. Fog is really a low-lying cloud that is near or touching the surface of the Earth.
  59. 59. Fog formation requires the presence of moisture, a gentle breeze, and a combination of warm and cold temperatures.
  60. 60. Fog is hazardous to aviation because it limits both ceiling (height above ground level of lowest layer of clouds that cover more than half the sky) and visibility (distance an object can be Seen with the unaided eye).
  61. 61. Fog at sea is a continual hazard to safe navigation.
  62. 62. Fog at Sea
  63. 63. The nautical "Rules of the Road" require that extra lookouts be stationed aboard ship in foggy conditions.
  64. 64. Fog at sea is frequently formed through a process known as advection. Fog is likely to develop when warm air that has passed over warm water moves to an area of colder water.
  65. 65. The horizontal transport of atmospheric properties The horizontal flow of air, water, etc. Advection
  66. 66. When warm moist air comes in contact with colder water, advection fog forms.
  67. 67. Advection fog is the name given to air-mass fog produced by air in motion, or to fog formed in one place and transported by wind to another. It will usually dissipate when the Sun rises.
  68. 68. Every Sailor is aware of the fogs that blanket the harbors and coastlines near these areas. Puget Sound San Francisco Los Angeles San Diego Newport New York Norfolk
  69. 69. Steam fog is a type of advection fog formed by air saturation.
  70. 70. A condition in the atmosphere corresponding to 100 percent relative humidity Saturation
  71. 71. In the far north, "sea smoke" can be seen in the late fall or winter when a river or pond "steams" as frigid air cools the water until it begins to form ice.
  72. 72. Fog caused by cold air flowing over a body of comparatively warm water, the vapor condensing in small convective columns near the water surface and giving the appearance of smoke or steam Sea Smoke
  73. 73. The heat that the Earth radiates causes radiation fog. It forms only at night, over a land surface. The Sun usually burns the fog away.
  74. 74. Fog produced by the nocturnal cooling of the surface boundary layer to a temperature at which its content of water vapor condenses Radiation Fog
  75. 75. The movement of cold air masses causes frontal fog. It is common in the upper Midwest.
  76. 76. A fog caused by the movement of two dissimilar air masses Frontal Fog
  77. 77. Q.1. What does the term hygroscopic nuclei mean? A.1. Particles that readily absorb moisture
  78. 78. A.2. Particles that are present in the air, such as dust, smoke, and pollen Q.2. What are examples of hygroscopic nuclei?
  79. 79. A.3. Raindrops are formed when moist air is cooled to the point where the moisture condenses into heavy drops. Q.3. How are raindrops formed?
  80. 80. A.4. Cirrus, cumulus, and stratus Q.4. What are the three basic types of clouds?
  81. 81. A.5. Fragmented or wind-blown Q.5. What does the prefix “fracto” mean?
  82. 82. A.6. Altocumulus clouds Q.6. What clouds are made of water droplets, sometimes laid out in parallel bands?
  83. 83. A.7. Changes in the atmospheric conditions Q.7. What accounts for the different shapes and altitudes of clouds?
  84. 84. A.8. Cirrus clouds Q.8. What clouds are often called “mares’ tails?”
  85. 85. A.9. High: above 20,000 ft. Middle: 7,000 to 20,000 ft. Low: surface to 7,000 ft. Q.9. What altitudes are associated with high, middle, and low clouds?
  86. 86. A.10. According to their appearance and altitude Q.10. How are clouds generally named?
  87. 87. A.11. Stratus, nimbostratus, and stratocumulus Q.11. What are the main types of low clouds?
  88. 88. A.12. Altocumulus and altostratus Q.12. What are the main types of middle clouds?
  89. 89. A.13. Cirrus, cirrostratus, and cirrocumulus Q.13. What are the main types of high clouds?
  90. 90. A.14. Thunderstorms and tornadoes Q.14. What type of weather is associated with cumulonimbus clouds?
  91. 91. Q.15. What weather condition follows cirrocumulus clouds?
  92. 92. Q.15. What weather condition follows cirrocumulus clouds? A.15. Precipitation

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