1. ATM OCN 100 Summer 2002 1 ATM OCN 100 - Fall 2001 LECTURE 13 (Con’t.) PRECIPITATION & the PRECIPITATION FORMATION PROCESS A. Introduction B. Background C. Observations & Measurements

2. ATM OCN 100 Summer 2002 2Announcements u Homework 4 is: –Posted has been posted on the Web at: –http://www.aos.wisc.edu/~hopkins/aos100/homework; http://www.aos.wisc.edu/~hopkins/aos100/homework –Due next Wednesday 7 Nov 2001. u First Hour Exam –If you have not picked up exam, please do so! –An exam statistics page is posted at: http://www.aos.wisc.edu/~hopkins/aos100/exams. http://www.aos.wisc.edu/~hopkins/aos100/exams u Homeworks 1- 3: –Please Pick up yours in front (at end of class). –Keys are posted on the Web at: –http://www.aos.wisc.edu/~hopkins/aos100/homework http://www.aos.wisc.edu/~hopkins/aos100/homework

3. MADISON’S CURRENT WEATHER at 900 AM CST FRI NOV 2 2001 Updated twice an hour at :05 and :25 Sky/Weather: SUNNY CLEAR Temperature: 53 F (11 C) Dew Point: 33 F (0 C) Relative Humidity: 46% Wind: VRB5 MPH Barometer: 30.01R

4. ATM OCN 100 Summer 2002 4 CURRENT IR MICHELLE

5. ATM OCN 100 Summer 2002 5 TD-15 CURRENT VISIBLE MICHELLE

6. ATM OCN 100 Summer 2002 6 MICHELLE CURRENT WATER VAPOR

7. ATM OCN 100 Summer 2002 7 Enhanced IR Satellite Image of Michelle (CIMSS-SSEC)

8. ATM OCN 100 Summer 2002 8 Forecast Track of Michelle

9. ATM OCN 100 Summer 2002 9 CURRENT IR MICHELLE

10. ATM OCN 100 Summer 2002 10 CURRENT VISIBLE MICHELLE

11. ATM OCN 100 Summer 2002 11 CURRENT WATER VAPOR MICHELLE

12. ATM OCN 100 Summer 2002 12 Enhanced IR Satellite Image of Michelle (CIMSS-SSEC)

13. ATM OCN 100 Summer 2002 13 Track of Michelle

14. ATM OCN 100 Summer 2002 14 Surface Weather Map from Today with Isobars & Fronts

15. ATM OCN 100 Summer 2002 15 Current Temperatures ( o F) & Isotherms

16. ATM OCN 100 Summer 2002 16 Current Dewpoints ( o F)

17. ATM OCN 100 Summer 2002 17 Tomorrow’s 7AM Forecast

18. ATM OCN 100 Summer 2002 18 Rule of thumb u If you can expect –Clear skies –Near Calm conditions u Then: –The afternoon dewpoint provides a good predictor of the following morning’s low temperature.

19. ATM OCN 100 Summer 2002 19 Surface Weather Map from Today with Isobars & Fronts

20. ATM OCN 100 Summer 2002 20 Current Temperatures ( o F) & Isotherms

21. ATM OCN 100 Summer 2002 21 Current Dewpoints ( o F)

22. ATM OCN 100 Summer 2002 22 Tomorrow’s 7AM Forecast

23. ATM OCN 100 Summer 2002 23 Rule of thumb u If you can expect –Clear skies –Near Calm conditions u Then: –The afternoon dewpoint provides a good predictor of the following morning’s low temperature.

24. ATM OCN 100 Summer 2002 24 Saturday Morning’s Low Overnight Low 33°F Fri AM Dewpoint 33 °F

25. ATM OCN 100 Summer 2002 25 This Morning’s Low Overnight Low 26°F Sun. Aftn. Dewpoint 23°F

26. MADISON’S CURRENT WEATHER Madison Weather at 1000 AM CDT 17 JUL 2002 Updated twice an hour at :05 and :25 Sky/Weather: PTSUNNY Temperature: 79 F (26 C) Dew Point: 65 F (18 C) Relative Humidity: 62% Wind: SW5 MPH Barometer: 30.07F (1018.3 mb)

27. ATM OCN 100 Summer 2002 27 Last 24 hrs in Madison FOG

28. ATM OCN 100 Summer 2002 28 CURRENT VISIBLE

29. ATM OCN 100 Summer 2002 29 CURRENT IR

30. ATM OCN 100 Summer 2002 30 Yesterday’s High Temperatures ( ° F)

31. ATM OCN 100 Summer 2002 31 Current Surface Weather Map with Isobars (“iso” = equal & “bar” = weight), Fronts and Radar

32. ATM OCN 100 Summer 2002 32 Current Surface Winds with Streamlines & Isotachs (“iso” = equal & “tach” = speed) L L H H LL H H L L H L L H

33. ATM OCN 100 Summer 2002 33 Yesterday’s High Temperatures ( o F) – (1961-90) Average High Temperatures

34. ATM OCN 100 Summer 2002 34 Current Temperatures ( o F) – 24 Hrs Ago Cold Advection + Drier Air

35. ATM OCN 100 Summer 2002 35 Current Temperatures ( ° F) & Isotherms (“iso” = equal +”therm” = temperature)

36. ATM OCN 100 Summer 2002 36 Current Dewpoints ( o F)

37. ATM OCN 100 Summer 2002 37 Sample Radiosonde Sites

38. ATM OCN 100 Summer 2002 38 RAPID CITY

39. ATM OCN 100 Summer 2002 39 GREEN BAY

40. ATM OCN 100 Summer 2002 40 IFR – Instrument Flight Rules Red Dots: Ceiling < 1000 ft or Visibility < 3 miles

41. ATM OCN 100 Summer 2002 41 Current Apparent Temperatures ( o F)

42. ATM OCN 100 Summer 2002 42 Forecast Heat Indices

43. ATM OCN 100 Summer 2002 43 Tomorrow AM Forecast Map

44. ATM OCN 100 Summer 2002 44 Announcements u Homework #3 is due today If you have ??, please see me.

45. ATM OCN 100 Summer 2002 45 ATM OCN 100 - Summer 2002 LECTURE 13 PRECIPITATION & the PRECIPITATION FORMATION PROCESS A. INTRODUCTION Statement of the Problems –What is precipitation? –Why is precipitation important? –How is precipitation formed? –How is precipitation measured?

46. ATM OCN 100 Summer 2002 46 B. BACKGROUND u Precipitation is –Liquid or solid water that falls from sky; –Examples: Rain, drizzle, snow, hail, ice pellets (sleet), freezing rain. u Precipitation is not: –Liquid or solid water that forms on surfaces; –Examples: Dew, frost, fog.

47. ATM OCN 100 Summer 2002 47 B. BACKGROUND (con’t.) u Importance of Precipitation u Meteorological Significance u Human Significance –Drought –Floods

48. ATM OCN 100 Summer 2002 48 C. OBSERVATIONAL MEASUREMENTS OF PRECIPITATION u Requirements –Away from obstacles; –Only precipitation above open collector is to be measured. u Direct observation by Rain gauges –Standard rain gauge; –Tipping bucket; –Weighing bucket. u Doppler Radar-estimated rainfall u Satellite-estimated rainfall

49. ATM OCN 100 Summer 2002 49 C. OBSERVATIONAL MEASUREMENTS OF PRECIPITATION u Requirements –Away from obstacles; –Only precipitation above open collector is to be measured. u Direct observation by Rain gauges … such as…

50. ATM OCN 100 Summer 2002 50 Simple Rain gauge

51. ATM OCN 100 Summer 2002 51 C. OBSERVATIONAL MEASUREMENTS OF PRECIPITATION u Requirements –Away from obstacles; –Only precipitation above open collector is to be measured. u Direct observation by Rain gauges –Standard rain gauge;

52. ATM OCN 100 Summer 2002 52 Standard Rain Gauge (right)

53. ATM OCN 100 Summer 2002 53 Standard Rain Gauge From J.M. Moran & WES Project of AMS

54. ATM OCN 100 Summer 2002 54 Collecting Funnel of a Standard Rain Gauge

55. ATM OCN 100 Summer 2002 55 Operation of Standard Rain Gauge (USA Today)

56. ATM OCN 100 Summer 2002 56 C. OBSERVATIONAL MEASUREMENTS OF PRECIPITATION u Requirements –Away from obstacles; –Only precipitation above open collector is to be measured. u Direct observation by Rain gauges –Standard rain gauge; –Tipping bucket;

57. ATM OCN 100 Summer 2002 57 Tipping Bucket Rain Gauge From J.M. Moran & WES Project of AMS

58. ATM OCN 100 Summer 2002 58 Tipping Bucket Rain Gauge (USA Today)

59. ATM OCN 100 Summer 2002 59 C. OBSERVATIONAL MEASUREMENTS OF PRECIPITATION u Requirements –Away from obstacles; –Only precipitation above open collector is to be measured. u Direct observation by Rain gauges –Standard rain gauge; –Tipping bucket; –Weighing bucket.

60. ATM OCN 100 Summer 2002 60 Weighing Bucket Gauge

61. ATM OCN 100 Summer 2002 61 “Rain Sensor” for NWS Automatic Weather Station

62. ATM OCN 100 Summer 2002 62 Automatic Weather Station in Snow Country

63. ATM OCN 100 Summer 2002 63 C. OBSERVATIONAL MEASUREMENTS OF PRECIPITATION u Measurement by Remote Sensors –Doppler Radar-estimated rainfall –Satellite-estimated rainfall

64. ATM OCN 100 Summer 2002 64 Measuring Rain with Weather Radar

65. ATM OCN 100 Summer 2002 65 Recent National Radar (Reflectivity Mode)

66. ATM OCN 100 Summer 2002 66 Doppler Radar Estimated Rainfall (in inches) for storm

67. ATM OCN 100 Summer 2002 67 Recent National Radar (Reflectivity Mode)

68. ATM OCN 100 Summer 2002 68 Doppler Radar Estimated Rainfall (in inches) for storm From 0700 CDT Monday 15 Jul 2002 to 0931 CDT Wed 15 Jul 2002

69. ATM OCN 100 Summer 2002 69

70. 70 Radar Estimated Rainfall [inches] from TS Allison in Houston, TX

71. ATM OCN 100 Summer 2002 71 Satellite-Derived Precipitation u Tropical Rainfall Measuring Mission (TRMM) –Precipitation radar –Microwave Imager –Visible and Infrared Scanner

72. ATM OCN 100 Summer 2002 72 Satellite-Derived Precipitation TRMM (Tropical Rainfall Measurement Mission)

73. ATM OCN 100 Summer 2002 73 Satellite-Derived Precipitation TRMM (Tropical Rainfall Measurement Mission)

74. ATM OCN 100 Summer 2002 74 How Deep is the Snow?

75. ATM OCN 100 Summer 2002 75 Snow Measurements u Snowfall –A snow board u Snowfall –Melt snow in rain gauge u Snow cover –A ruler

76. ATM OCN 100 Summer 2002 76 This Deep !

77. ATM OCN 100 Summer 2002 77 D. BUILDING A RAINDROP u Requirements for Raindrop Formation “Not all clouds precipitate!” –Build a drop that will fall; –Rain drop must be made rapidly. u The beginning –Cloud droplet formation - Nucleation (Birth) –Plenty of small cloud droplets r cloud = 20  m

78. ATM OCN 100 Summer 2002 78 A RAINDROP u A MYTH From “Bad Rain” - Alistair B. Fraser

79. ATM OCN 100 Summer 2002 79 A RAINDROP u A MYTH u But…

80. ATM OCN 100 Summer 2002 80 D. BUILDING A RAINDROP (con’t.) u Terminal velocity –Maximum speed attained by a falling object; –Caused by frictional drag from air; –Related to the mass to surface area ratio; –Hence, dependent upon cloud droplet size.

81. ATM OCN 100 Summer 2002 81

82. 82 D. BUILDING A RAINDROP (con’t.) u The outcome –Typical Rain Drop Sizes (2 - 4 mm. diameter) u Factors opposing Precipitation –Cloud-producing updrafts greater than droplet’s terminal velocity; –Dry atmosphere below cloud base may evaporate droplet to form VIRGA. where...

83. ATM OCN 100 Summer 2002 83 D. BUILDING A RAINDROP (con’t.) u Terminal velocity –Dependent upon size u Amount of water needed depends upon: –Volume of spherical droplet; –or equivalently, the cube of the radius (Since V = 4/3  r 3, where r = radius).

84. ATM OCN 100 Summer 2002 84 D. BUILDING A RAINDROP (con’t.)  So if r cloud = 20  m, an increase to r rain = 200  m: –then a tenfold increase in radius (200  m Vs. 20  m ) causes a Volume increase that would be 10 3 = 1000 times larger.

85. ATM OCN 100 Summer 2002 85 D. BUILDING A RAINDROP (con’t.) u Requirements –Need to build Rain Drop from Cloud Droplet –But… amount of water needed is proportional to the cube of the radius! u Factors opposing Precipitation –Cloud-producing updrafts greater than droplet’s terminal velocity; –Dry atmosphere below cloud base may evaporate droplet to form VIRGA. where...

86. ATM OCN 100 Summer 2002 86 D. BUILDING A RAINDROP (con’t.) u Factors opposing Precipitation –Cloud-producing updrafts greater than droplet’s terminal velocity; –Dry atmosphere below cloud base may evaporate droplet to form VIRGA.

87. ATM OCN 100 Summer 2002 87Virga

88. 88 A Convective Rainshower

89. ATM OCN 100 Summer 2002 89 E. POSSIBLE PRECIPITATION MECHANISMS (Growth of Liquid rain drops) u The current proposed mechanisms: –Simple Condensation by Diffusion Process –The Collision - Coalescence Process –The Ice Crystal or Bergeron-Findeisen Process or specifically,... or specifically,...

90. ATM OCN 100 Summer 2002 90 PRECIPITATION MECHANISM: CONDENSATION-DIFFUSION PROCESS u Based upon H 2 0 vapor molecules condensing upon cloud droplets; u Competing Effects –Curvature Effect –Solute Effect u Condensation needs to overcome surface tension of droplet; u Process would take 24 to 48 hours; u Hence, process is too slow!

91. ATM OCN 100 Summer 2002 91 PRECIPITATION MECHANISM: COLLISION-COALESCENCE PROCESS  Requires droplets of various sizes, with some greater than 20  m diameter; u Large droplets have greater fall speed; Figure 8.2 Moran & Morgan (1997)

92. ATM OCN 100 Summer 2002 92 COLLISION-COALESCENCE THEORY (con’t.) u Different sized droplets have different surface electrostatic charges; u Large droplet has a wake “low”; u Thus, large droplets collect smaller droplets and form a rain drop.

93. ATM OCN 100 Summer 2002 93 PRECIPITATION MECHANISM: ICE CRYSTAL ( or Bergeron-Findeisen) PROCESS u Requires a mixture of ice crystals and supercooled liquid droplets; –supercooled droplet remains a liquid at -40 o C (-40 o F) < T < 0 o C (32 o F); –smaller droplets are more frequently supercooled.

94. ATM OCN 100 Summer 2002 94 Saturation Vapor Pressure as a Function of Temperature See Fig. 6.3 Moran & Morgan, 1997

95. ATM OCN 100 Summer 2002 95

96. 96 ICE CRYSTAL THEORY (con’t.) u Saturation vapor pressure over supercooled liquid >> over ice at same T; u Therefore, ice crystal grows at expense of supercooled water droplet. Figure 8.3 Moran & Morgan (1997)

97. ATM OCN 100 Summer 2002 97 F. PRECIPITATION TYPES u Distinguishing Features of Precipitation Types –Liquid (Rain, Drizzle) –Frozen (Snow, Ice Pellets, Hail) –Freezing (Freezing Rain, Freezing Drizzle) where --

98. ATM OCN 100 Summer 2002 98 LIQUID PRECIPITATION National Weather Service

99. ATM OCN 100 Summer 2002 99 FROZEN PRECIPITATION National Weather Service

100. ATM OCN 100 Summer 2002 100Snow

101. 101 Recall PHYSICAL PHASES of H 2 O u Solid (Ice) -- Note Hexagonal (6 sided) Structure

102. ATM OCN 100 Summer 2002 102 Varieties of Snowflakes

103. ATM OCN 100 Summer 2002 103 Varieties of Snowflakes (USA Today) See Fig. 8.6, Moran & Morgan, 1997

104. ATM OCN 100 Summer 2002 104 Varieties of Snowflakes See Fig. 8.6, Moran & Morgan, 1997

105. ATM OCN 100 Summer 2002 105 FREEZING PRECIPITATION National Weather Service

106. ATM OCN 100 Summer 2002 106 Freezing Rain

107. ATM OCN 100 Summer 2002 107 Freezing Rain/Ice Storm

108. ATM OCN 100 Summer 2002 108 Hail Stones

109. ATM OCN 100 Summer 2002 109 Hail Stones

110. ATM OCN 100 Summer 2002 110 Hail Storm

111. ATM OCN 100 Summer 2002 111 Snow Event

112. ATM OCN 100 Summer 2002 112 Rain Event

113. ATM OCN 100 Summer 2002 113 Freezing Rain Event

114. ATM OCN 100 Summer 2002 114 Ice Pellet (Sleet) Formation

115. ATM OCN 100 Summer 2002 115 Summary of Precipitation Type Formation

116. ATM OCN 100 Summer 2002 116 Freezing Rain Climatology

117. ATM OCN 100 Summer 2002 117 G. PRECIPITATION CLIMATOLOGY - Annual

118. ATM OCN 100 Summer 2002 118 G. PRECIPITATION CLIMATOLOGY - July

119. ATM OCN 100 Summer 2002 119 G. PRECIPITATION CLIMATOLOGY - January

120. ATM OCN 100 Summer 2002 120 H. WEATHER MODIFICATION BACKGROUND u Statement of Problem –Why no precipitation? –Can humans cause rain? u For precipitation, need: –sufficient atmospheric humidity; –a cloud; –sufficiently large raindrops/snowflakes to fall & reach ground as rain or snow.

121. ATM OCN 100 Summer 2002 121 INTENTIONAL ARTIFICIAL WEATHER MODIFICATION u Goals –Stimulate Precipitation –Dissipate Clouds & Fog –Suppress Hail –Modify Hurricanes

122. ATM OCN 100 Summer 2002 122 C. WEATHER MODIFICATION (con’t.) u Precipitation Stimulation Techniques - "Cloud seeding" –Early Weather Modification Techniques –Modern Precipitation Stimulation Strategies –Problems F Scientific F Legal

123. ATM OCN 100 Summer 2002 123 TYPICAL STRATEGIES u WARM CLOUDS –Add large hygroscopic nuclei. u COLD CLOUDS –Freeze all supercooled droplets with Dry Ice (Solid CO 2 ); –Add freezing nuclei with ice-like crystal structure with Silver Iodide (AgI).

124. ATM OCN 100 Summer 2002 124 ATM OCN 100 - Summer 2001 LECTURE 13 (Con’t.) PRECIPITATION & the PRECIPITATION FORMATION PROCESS A. Introduction B. Background C. Observations & Measurements D. Building a Raindrop E. Possible Precipitation Mechanisms F. Precipitation Types G. Precipitation Climatology H. Artificial Weather Modification