+Forms of Condensation andPrecipitation Chapter 5
+5.1 Cloud Formation
+ Cloud Formation A cloud  is a visible aggregate of small water  droplets or ice crystals that are suspended in  the atm...
+ Cloud Formation Condensation  aloft: Adiabatic cooling causes clouds to form as  water vapor condenses in the atmosphe...
+ Cloud Formation Growth   of cloud droplets: Hygroscopic (water-seeking) nuclei are most  effective for condensation. ...
+5.2 Cloud Classification
+ Cloud Classification Clouds     are classified on the basis of two criteria. 1. Form:  Cirrusare high, white, and thin...
+ Cloud Classification 2.   Height:     High clouds are above 6000 m.     Middle clouds range between 2000–6000 m.     ...
+ Cloud Classification
+ Cloud Classification
+ Cloud Classification- High Clouds Low  temp and small amount of water vapor at  high altitudes equal high clouds, thin,...
+
+ Cloud Classification- High Clouds Cirrostratus   Transparent,whitish cloud veils with fibrous or    sometimes smooth a...
+
+ Cloud Classification- High Clouds Cirrocumulus   White patches composed of small cells or   ripples resembling fish sc...
+
+ Cloud Classification- Medium Clouds Altocumulus   Tend to form in large patches composed of    rounded masses or rolls...
+
+ Cloud Classification- Medium Clouds Altostratus   Formless   layer of grayish clouds that cover all    or portions of ...
+
+ Cloud Classification- Low Clouds Stratus   Uniform   layer covers much of the sky   Ones with scalloped bottom and ap...
+CloudClassification- Low Clouds  Nimbostratus   Rain   clouds
+ Clouds of Vertical Development Cumulus    humilis   Dense,  billowly clouds with tops resembling    cauliflower. Often...
+
+ Clouds of Vertical Development Cumulonimbus   Large  dense billowly clouds of considerable    vertical extent in the f...
+
+ Cloud Classification Cloud   varieties:   Uncinus  are hooked shaped clouds, often    precursors to bad weather.   Fr...
+ Cloud Classification
+5.3 Types of Fog
+ Types of Fog Fog is defined as a cloud with its base at or  very near the ground. Fog  results from cooling or when ai...
+ Fog Formed by Cooling  Radiation           fog results from radiation cooling of the  ground and adjacent air.   Night...
+
+ Fog Formed by Cooling  Advection fog is a blanket of fog caused by warm,  moist air blowing over a cold surface.   Som...
+
+ Fog Formed by Cooling Upslope  fog is created when relatively humid  air moves up a sloping landform or up the  steep s...
+ Fog Formed by Cooling There   are two types of evaporation fog.   Frontal (precipitation) fog    Occurs when rain dro...
+ Fog Formed by Cooling Steam   fog   Occurs when cool air moves over warm water.   Moisture evaporates and saturates t...
+
+5.4 How Precipitation Forms
+ How Precipitation Forms  Clouddroplets are about 20 micrometers in  diameter. A human hair is about 75  micrometers  A...
+ How Precipitation Forms
+ How Precipitation Forms  Process that generates precipitation in the middle  latitudes  The Bergeron Process depends o...
+ How Precipitation Forms So,  imagine a cloud at -10°C where each ice  crystal (snow crystal) is surrounded by thousands...
+ How Precipitation Forms So the growth of ice crystals is fed by  continued evaporation of liquid droplets When    ice ...
+ How Precipitation Forms The  type of precipitation (snow, sleet, rain, or  freezing rain) depends on the temperature in...
+ How Precipitation Forms The Bergeron process  (precipitation from cold  clouds) depends on the  coexistence of water  v...
+ How Precipitation Forms The collision-coalescence process  (precipitation from warm clouds) occurs as  copious rainfall...
+ How Precipitation Forms
+ How Precipitation Forms
+5.5 Forms of Precipitation
+    Forms of Precipitation
+ Forms of Precipitation Rainis restricted to droplets of water with a  diameter at least 0.5mm. Cloudbursts   are unusu...
+ Forms of Precipitation Virga   is rain that evaporates above ground. Fallstreaks are ice crystals that sublime in the ...
+Virga
+ Forms of Precipitation  Snow is precipitation in the form of ice crystals or  aggregates of ice crystals.  Size,      ...
+Forms of PrecipitationSleet   is clear to  translucent particles of  ice, rain drops freeze  while falling.Freezing   r...
+ Forms of Precipitation Hail is precipitation in the  form of hard, rounded  pellets of ice.   Itis produced in    cumu...
+ Forms of Precipitation Rime  is a deposit of ice crystals, formed on  surface objects by super-cooled fog or cloud  dro...
+5.6 Precipitation Measurement
+ Precipitation Measurement Standard   instruments:   A standard rain gauge catches rain water and   conducts it through...
+ Precipitation Measurement A tipping  bucket has two compartments (or  buckets). When one bucket fills, it tips and  emp...
+ Precipitation Measurement  Whenmeasuring snowfall, two measurements are  normally taken.   The depth is measured with ...
+5.7 Intentional WeatherModification
+ Intentional Weather Modification Intentional  weather modification, such as  cloud seeding, is deliberate human  interv...
+ Intentional Weather Modification  Hailsuppression has been shown to be  ineffective.   Anti-hail cannons produced a lo...
+ Intentional Weather Modification Several   methods of frost prevention are being  used.   Water  sprinklers add heat f...
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Forms of Condensation and Precipitation

  1. 1. +Forms of Condensation andPrecipitation Chapter 5
  2. 2. +5.1 Cloud Formation
  3. 3. + Cloud Formation A cloud is a visible aggregate of small water droplets or ice crystals that are suspended in the atmosphere above the earth’s surface Lifting condensation level  The ascending parcel of air is cooled to its dew point temperature and triggers condensation
  4. 4. + Cloud Formation Condensation aloft: Adiabatic cooling causes clouds to form as water vapor condenses in the atmosphere. The air becomes saturated and there must be a surface. Condensation nuclei act as surfaces, on which the water vapor can condense.
  5. 5. + Cloud Formation Growth of cloud droplets: Hygroscopic (water-seeking) nuclei are most effective for condensation. Growth is rapid at first, then slows as water vapor is consumed. Hygrophobic (water-fearing) nuclei are not efficient condensation nuclei but could droplets will form on them when the relative humidity reaches 100%
  6. 6. +5.2 Cloud Classification
  7. 7. + Cloud Classification Clouds are classified on the basis of two criteria. 1. Form:  Cirrusare high, white, and thin forming delicate veil like patches or wisplike strands often have a feathery appearance  Cumulus clouds are globular, usually exhibiting a flat base and appear as rising domes or towers.  Stratus clouds are best described as layers or sheets covering much of the sky.
  8. 8. + Cloud Classification 2. Height:  High clouds are above 6000 m.  Middle clouds range between 2000–6000 m.  Low clouds are at altitudes of less than 2000 m.  Clouds of vertical development extend upward to span more than one height range.
  9. 9. + Cloud Classification
  10. 10. + Cloud Classification
  11. 11. + Cloud Classification- High Clouds Low temp and small amount of water vapor at high altitudes equal high clouds, thin, white and made of ice crystals Cirrus  Delicate, icy filaments. Winds cause the filaments to bend or curl
  12. 12. +
  13. 13. + Cloud Classification- High Clouds Cirrostratus  Transparent,whitish cloud veils with fibrous or sometimes smooth appearance covering whole sky.  Produce halos around the the sun or moon
  14. 14. +
  15. 15. + Cloud Classification- High Clouds Cirrocumulus  White patches composed of small cells or ripples resembling fish scales
  16. 16. +
  17. 17. + Cloud Classification- Medium Clouds Altocumulus  Tend to form in large patches composed of rounded masses or rolls that may or may not merge  Composed of water not ice droplets  The individual cells have a more distinct outline
  18. 18. +
  19. 19. + Cloud Classification- Medium Clouds Altostratus  Formless layer of grayish clouds that cover all or portions of the sky.  Sun is visible as a big bright spot with the edge of it’s disc not discernible; no halos  Infrequent snow or drizzle.  Commonly associated with approaching warm fronts thicken into nimbostratus (which = lots of rain)
  20. 20. +
  21. 21. + Cloud Classification- Low Clouds Stratus  Uniform layer covers much of the sky  Ones with scalloped bottom and appears as long parallel rolls or broken patches are called stratocumulus
  22. 22. +CloudClassification- Low Clouds  Nimbostratus  Rain clouds
  23. 23. + Clouds of Vertical Development Cumulus humilis  Dense, billowly clouds with tops resembling cauliflower. Often form on clear days  Known as fair weather clouds  Humilis are smaller
  24. 24. +
  25. 25. + Clouds of Vertical Development Cumulonimbus  Large dense billowly clouds of considerable vertical extent in the form of huge vertically towers  Tops spread out into an anvil shape  Towers produce heavy precipitation with lightening, thunder, and occasionally hail
  26. 26. +
  27. 27. + Cloud Classification Cloud varieties:  Uncinus are hooked shaped clouds, often precursors to bad weather.  Fractus or fractured clouds are stratus or cumulus clouds that appear broken.  Mammatus clouds have udder-shaped protuberances on their bottom surfaces and are associated with stormy weather.  Lenticular clouds are lens shaped and are common in rugged or mountainous topographies.
  28. 28. + Cloud Classification
  29. 29. +5.3 Types of Fog
  30. 30. + Types of Fog Fog is defined as a cloud with its base at or very near the ground. Fog results from cooling or when air becomes saturated through the addition of water vapor  Radiation  Advection  Upslope  Evaporative
  31. 31. + Fog Formed by Cooling  Radiation fog results from radiation cooling of the ground and adjacent air.  Night time phenomena requiring clear skies and relatively high humidity  The high humidity can cause a small amount of cooling to lower the temperature to the dew point.  To be extensive, there should be a slight breeze.  It is usually thickest in valleys.
  32. 32. +
  33. 33. + Fog Formed by Cooling  Advection fog is a blanket of fog caused by warm, moist air blowing over a cold surface.  Some turbulence is needed (10–30 kph winds).  Turbulence facilitates cooling through a thicker layer of air and carries it to greater heights  Wintertime fog in the midwest  This fog is thick and produces hazardous driving conditions
  34. 34. +
  35. 35. + Fog Formed by Cooling Upslope fog is created when relatively humid air moves up a sloping landform or up the steep slopes of a mountain.  Theupward flow causes the air to expand and cool adiabatically resulting in fog.
  36. 36. + Fog Formed by Cooling There are two types of evaporation fog.  Frontal (precipitation) fog  Occurs when rain droplets falling from relatively warm air above a frontal surface evaporates into the cooler air below and causes it to become saturated.
  37. 37. + Fog Formed by Cooling Steam fog  Occurs when cool air moves over warm water.  Moisture evaporates and saturates the air above it.  Rising water vapor meets the cool air, condenses and rises. Looks like steam.  Steam fog is very common over lakes.
  38. 38. +
  39. 39. +5.4 How Precipitation Forms
  40. 40. + How Precipitation Forms  Clouddroplets are about 20 micrometers in diameter. A human hair is about 75 micrometers  A rain droplet is about 2 mm or 100 times the average cloud droplet  Volume is 1 million times greater
  41. 41. + How Precipitation Forms
  42. 42. + How Precipitation Forms  Process that generates precipitation in the middle latitudes  The Bergeron Process depends on the process of the coexistence of water vapor, liquid cloud droplets and ice crystals.  Cloud droplets do not freeze at 0°C. It freezes at -40°C. it is super cooled.  The saturation vapor pressure above ice crystals is slightly lower than above super cooled liquid droplet
  43. 43. + How Precipitation Forms So, imagine a cloud at -10°C where each ice crystal (snow crystal) is surrounded by thousands of liquid droplets. Because air is saturated at 100% with respect to liquid water, it will be super saturated (above 100%) with respect to the newly formed ice crystals. At this result of this supersaturation, the ice crystals collect water, lowering relative humidity, the water droplets shrink to replenish what was lost
  44. 44. + How Precipitation Forms So the growth of ice crystals is fed by continued evaporation of liquid droplets When ice gets large enough they fall, they grow as they intercept cloud droplets on their fall. A chain reaction ensues and produces many snow crystals= snow flakes
  45. 45. + How Precipitation Forms The type of precipitation (snow, sleet, rain, or freezing rain) depends on the temperature in the lower few km of the atmosphere When the surface temperature is above 39°F snow usually melts before it hits the ground
  46. 46. + How Precipitation Forms The Bergeron process (precipitation from cold clouds) depends on the coexistence of water vapor, liquid cloud droplets, and ice crystals
  47. 47. + How Precipitation Forms The collision-coalescence process (precipitation from warm clouds) occurs as copious rainfall associated with clouds located below the freezing level (called warm clouds), especially in the tropics.  Small droplets hit other droplets and become larger.  They collide with more droplets and their falling velocity increases.
  48. 48. + How Precipitation Forms
  49. 49. + How Precipitation Forms
  50. 50. +5.5 Forms of Precipitation
  51. 51. + Forms of Precipitation
  52. 52. + Forms of Precipitation Rainis restricted to droplets of water with a diameter at least 0.5mm. Cloudbursts are unusually heavy rainfalls. Drizzleare fine, uniform droplets with a diameter less than 0.5mm. (not really considered rain)
  53. 53. + Forms of Precipitation Virga is rain that evaporates above ground. Fallstreaks are ice crystals that sublime in the dry air below Mist contains the smallest droplets.
  54. 54. +Virga
  55. 55. + Forms of Precipitation  Snow is precipitation in the form of ice crystals or aggregates of ice crystals.  Size, shape and concentration depend to great extent on the temp at which they form  Low temperature, the moisture is low = very light fluffy snow made up of individual 6 sided crystals  Warmer temperature at about 23°F, ice crystals join together into large clumps of tangled crystals
  56. 56. +Forms of PrecipitationSleet is clear to translucent particles of ice, rain drops freeze while falling.Freezing rain (glaze) are rain drops that become super-cooled, hit a surface, and freeze immediately.
  57. 57. + Forms of Precipitation Hail is precipitation in the form of hard, rounded pellets of ice.  Itis produced in cumulonimbus clouds.  Hail stones begin as small ice pellets and grow as they are propelled by updrafts and downdrafts through the cloud.
  58. 58. + Forms of Precipitation Rime is a deposit of ice crystals, formed on surface objects by super-cooled fog or cloud droplets.  Itoccurs when the surface temperature of an object is below freezing.
  59. 59. +5.6 Precipitation Measurement
  60. 60. + Precipitation Measurement Standard instruments:  A standard rain gauge catches rain water and conducts it through a narrow opening into a cylindrical measuring tube.  The gauge is 20 cm in diameter and can measure rainfall to the nearest 0.025 cm.  < 0.025 cm = trace
  61. 61. + Precipitation Measurement A tipping bucket has two compartments (or buckets). When one bucket fills, it tips and empties its water and the other bucket takes its place at the funnel. A weighing gauge collects rain fall in a cylinder that rests on a spring balance. As the cylinder fills, the movement is transmitted to a pen that records the data.
  62. 62. + Precipitation Measurement  Whenmeasuring snowfall, two measurements are normally taken.  The depth is measured with a calibrated stick.  To obtain the water equivalent, snow is melted and then weighed or measured as rain.  Weather radar uses radio waves to measure precipitation.  The radio waves penetrate small droplets, but are reflected off larger ones. Echoes are sent back and displayed.
  63. 63. +5.7 Intentional WeatherModification
  64. 64. + Intentional Weather Modification Intentional weather modification, such as cloud seeding, is deliberate human intervention to influence processes that constitute the weather.  Snow and rain making  Silver iodide crystals act as freezing nuceli.  Fog and cloud dispersal  Cloud seeding with dry ice into super-cooled fog or stratus clouds helps to disperse them to improve visibility.
  65. 65. + Intentional Weather Modification  Hailsuppression has been shown to be ineffective.  Anti-hail cannons produced a loud whistling noise and a large smoke ring thought to suppress hail.  Cloud seeding with silver iodide crystals was also employed to disrupt the growth of hailstones.
  66. 66. + Intentional Weather Modification Several methods of frost prevention are being used.  Water sprinklers add heat from water and from the latent heat of fusion when the water freezes.  Air mixing uses wind machines to mix warm and cool air.  Orchard heaters produce the most successful results, but fuel cost can be significant.

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