1. ATM OCN 100 Summer 2002 1 ATM OCN 100 - Summer 2002 LECTURE 11 (con’t.) FORMATION OF CLOUDS, FOG, DEW & FROST A. Introduction & Background B. Requirements for Droplet Formation C. Mechanisms for Cloud, Fog, Dew Formation D. Low-level Saturation Processes E. Mechanisms for Cloud (Fog) Formation

2. ATM OCN 100 Summer 2002 2 Announcements 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; u Homework 3 is: – posted on the Web at: –http://www.aos.wisc.edu/~hopkins/aos100/homework; –Due ??? (Stay tuned!). Homeworks 1 & 2 –Please Pick up yours in front (at end of class).

3. MADISON’S CURRENT WEATHER at 900 AM CDT WED OCT 24 2001 Updated twice an hour at :05 and :25 Sky/Weather: DRIZZLE Temperature: 57 F (13 C) Dew Point: 56 F (13 C) Relative Humidity: 96% Wind: W6 MPH Barometer: 29.42R

4. ATM OCN 100 Summer 2002 4 CURRENT IR

5. ATM OCN 100 Summer 2002 5 CURRENT VISIBLE

6. ATM OCN 100 Summer 2002 6 CURRENT WATER VAPOR

7. ATM OCN 100 Summer 2002 7 Surface Weather Map from Today with Isobars & Fronts

8. ATM OCN 100 Summer 2002 8 Current Temperatures ( o F) & Isotherms

9. ATM OCN 100 Summer 2002 9 Current Dewpoints ( o F)

10. ATM OCN 100 Summer 2002 10 Last 24 hrs in Madison

11. ATM OCN 100 Summer 2002 11 IFR – Instrument Flight Rules Red Dots: Ceiling < 1000 ft or Visibility < 3 miles

12. ATM OCN 100 Summer 2002 12 Tomorrow’s 7AM Forecast

13. ATM OCN 100 Summer 2002 13 Surface Weather Map from Today with Isobars & Fronts

14. ATM OCN 100 Summer 2002 14 Current Temperatures ( o F) & Isotherms

15. ATM OCN 100 Summer 2002 15 Current Dewpoints ( o F)

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

17. ATM OCN 100 Summer 2002 17

18. 18

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20. 20 Current Precipitable Water (in mm) from GOES Satellites

21. ATM OCN 100 Summer 2002 21 Last 24 hrs in Madison

22. ATM OCN 100 Summer 2002 22 Previous 24 hrs in Madison

23. ATM OCN 100 Summer 2002 23 Surface Weather Map from This AM with Isobars & Fronts

24. ATM OCN 100 Summer 2002 24 IFR – Instrument Flight Rules Ceiling < 1000 ft or Visibility < 3 miles

25. ATM OCN 100 Summer 2002 25 IFR – Instrument Flight Rules Ceiling < 1000 ft or Visibility < 3 miles

26. MADISON’S CURRENT WEATHER Madison Weather at 1000 AM CDT 15 JUL 2002 Updated twice an hour at :05 and :25 Sky/Weather: SUNNY Temperature: 80 F (26 C) Dew Point: 60 F (15 C) Relative Humidity: 50% Wind: VRB6 MPH Barometer: 30.12F (1019.10 mb)

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

28. ATM OCN 100 Summer 2002 28 Last 24 hrs in Madison

29. ATM OCN 100 Summer 2002 29 Last 24 hrs in Madison

30. ATM OCN 100 Summer 2002 30 Last Night’s Green Bay Sounding

31. ATM OCN 100 Summer 2002 31 CURRENT VISIBLE T.D. #1

32. ATM OCN 100 Summer 2002 32 T.D. #1 CURRENT IR

33. ATM OCN 100 Summer 2002 33 CURRENT WATER VAPOR

34. ATM OCN 100 Summer 2002 34 Current Surface Weather Map with Isobars (“iso” = equal & “bar” = weight), Fronts and Radar T.D. #1

35. ATM OCN 100 Summer 2002 35 Forecast for T.D. 1

36. ATM OCN 100 Summer 2002 36

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38. 38 Yesterday’s High Temperatures ( ° F)

39. ATM OCN 100 Summer 2002 39 Current Surface Weather Map with Isobars (“iso” = equal & “bar” = weight), Fronts and Radar T.D. #1

40. ATM OCN 100 Summer 2002 40 Current Surface Winds with Streamlines & Isotachs (“iso” = equal & “tach” = speed) L L H H L L L H H L

41. ATM OCN 100 Summer 2002 41 Yesterday’s High Temperatures ( o F) – (1961-90) Average High Temperatures

42. ATM OCN 100 Summer 2002 42 Current Temperatures ( o F) – 24 Hrs Ago Cold Advection + Drier Air

43. ATM OCN 100 Summer 2002 43 Current Temperatures ( ° F) & Isotherms (“iso” = equal +”therm” = temperature)

44. ATM OCN 100 Summer 2002 44 Current Dewpoints ( o F)

45. ATM OCN 100 Summer 2002 45 IFR – Instrument Flight Rules Red Dots: Ceiling < 1000 ft or Visibility < 3 miles

46. ATM OCN 100 Summer 2002 46 Current Apparent Temperatures ( o F)

47. ATM OCN 100 Summer 2002 47 Tomorrow AM Forecast Map

48. ATM OCN 100 Summer 2002 48 Announcements u Homework #3 is due next Thurs. 18 July 2002 u If you have ??, please see me.

49. ATM OCN 100 Summer 2002 49 ATM OCN 100 - Summer 2002 LECTURE 11 FORMATION OF CLOUDS, FOG, DEW & FROST A. INTRODUCTION – What is a cloud? – Historical Perspective – Why are clouds important?

50. ATM OCN 100 Summer 2002 50 ATM OCN 100 - Summer 2002 LECTURE 11 FORMATION OF CLOUDS, FOG, DEW & FROST A. Introduction B. Background F Cloud – A visible aggregation of water droplets &/or ice crystals suspended in air above ground. F Fog – A low-level cloud at ground level that reduces horizontal visibility. F Dew & Frost – Surface condensation/deposition phenomena.

51. ATM OCN 100 Summer 2002 51 BACKGROUND: CLOUDS, FOG, DEW & FROST u Cloud – A visible aggregation of water droplets &/or ice crystals suspended in air above ground. u Fog – A low-level cloud at ground level that reduces horizontal visibility. u Dew & Frost – Surface condensation/deposition phenomena.

52. ATM OCN 100 Summer 2002 52 B. REQUIREMENTS FOR FORMATION of DROPLETS u Statement of Practical Problems u Need for Saturation Conditions u Low-level Condensation Process in Dew Formation u Special Requirements in Free Air u Condensation Process in Cloud Formation

53. ATM OCN 100 Summer 2002 53 C. MECHANISMS for CLOUD (FOG, DEW or FROST) FORMATION u To Saturate – R.H. needs to reach 100% (or T air = T dew ) u Formation Options – Add water vapor (increase T dew to T air ); – Cool air (reduce T air to T dew ). where...

54. ATM OCN 100 Summer 2002 54 OPTIONS TO SATURATE THE AIR u Evaporation Mechanisms Adding water vapor to saturation (increase dewpoint to air temperature) – Require abundant liquid water source (e.g., ocean, lake, or lush vegetation) ; – Mix moisture upward from surface by air motion.

55. ATM OCN 100 Summer 2002 55 OPTIONS TO SATURATE THE AIR (con’t.) u Cooling Mechanisms Cool air to saturation (reduce air temperature to dewpoint) by: –Radiational Cooling – Expansional Cooling – Evaporative Cooling – Advection Cooling - Horizontal Transport

56. ATM OCN 100 Summer 2002 56 D. LOW LEVEL SATURATION PROCESSES & PHENOMENA u Dew & Frost – Definitions – Formation – Comparison & Contrasts – Significance

57. ATM OCN 100 Summer 2002 57Dew

58. 58Hoarfrost

59. 59 Frost

60. 60 E. CLOUD (or FOG) FORMATION REQUIREMENTS u A Problem – Dipolar nature of water molecules –Leads to difficulty in condensing in clean air u Supersaturation – Condition where R.H. > 100%. u Mechanism for Condensation Cloud Condensation Nuclei

61. ATM OCN 100 Summer 2002 61 CLOUD CONDENSATION NUCLEI u Provide sites for condensation u Requirement - – Hygroscopic substances (Water loving) u Types of Condensation Nuclei – Sea salt – Combustion products – Anthropogenic substances

62. ATM OCN 100 Summer 2002 62 Aerosols from Sea Spray

63. ATM OCN 100 Summer 2002 63 Aerosols from Wildfires

64. ATM OCN 100 Summer 2002 64 Aerosols from Urban Pollution

65. ATM OCN 100 Summer 2002 65 E. MECHANISMS for CLOUD or FOG FORMATION (con’t.) u u Cooling Mechanisms – – Expansional Cooling – – Evaporative Cooling – – Advection Cooling - Horizontal Transport – – Radiational Cooling

66. ATM OCN 100 Summer 2002 66 Clouds accompanying a F-18 jet breaking the Sound Barrier

67. ATM OCN 100 Summer 2002 67 EXPANSIONAL COOLING SPECIFICS u Review of adiabatic processes u Dry adiabatic lapse rate – No H 2 O phase change when R.H. < 100%; – DALR  10 C o per 1000 m  (5.5 F o per 1000 ft); – Reversible process cooling by DALR during ascent = warming by DALR during descent.

68. ATM OCN 100 Summer 2002 68 Response of Ascent/Descent of Air Parcel: Dry Adiabatic Lapse Rate See Fig. 6.8 Moran & Morgan (1997)

69. ATM OCN 100 Summer 2002 69 Comparison of Dry & Saturation (Moist) Adiabatic Lapse Rates See Fig. 6.9 Moran & Morgan (1997)

70. ATM OCN 100 Summer 2002 70 EXPANSIONAL COOLING SPECIFICS (con’t.) u Saturation (moist) adiabatic lapse rate – Involves H 2 O phase change when R.H. = 100%; – Release of latent heat of condensation into parcel diminishes cooling effect by adiabatic expansion; – SALR  6 to 7 C o per 1000 m  (3 F o per 1000 ft); – Process may not be reversible.

71. ATM OCN 100 Summer 2002 71 WAYS TO LIFT FOR EXPANSIONAL COOLING u Dynamic Lifting – In surface low pressure systems; – Along frontal surfaces. u Lifting by Convection – Localized heating – Ascending convection currents  Mechanical Lifting Over mountain barriers (or orographic lifting)

72. ATM OCN 100 Summer 2002 72 WAYS TO LIFT FOR EXPANSIONAL COOLING u Dynamic Lifting – In surface low pressure systems; – Along frontal surfaces.

73. ATM OCN 100 Summer 2002 73 Dynamic Lifting

74. ATM OCN 100 Summer 2002 74 WAYS TO LIFT FOR EXPANSIONAL COOLING u Dynamic Lifting – In surface low pressure systems; – Along frontal surfaces. u Lifting by Convection – Localized heating – Ascending convection currents

75. ATM OCN 100 Summer 2002 75 Lifting by Convection Lifting by Convection

76. ATM OCN 100 Summer 2002 76 WAYS TO LIFT FOR EXPANSIONAL COOLING u Dynamic Lifting – In surface low pressure systems; – Along frontal surfaces. u Lifting by Convection – Localized heating – Ascending convection currents  Mechanical Lifting Over mountain barriers (or orographic lifting)

77. ATM OCN 100 Summer 2002 77 Mechanical (orographic) Lifting

78. ATM OCN 100 Summer 2002 78 AN EXAMPLE Air Flow over a mountain

79. ATM OCN 100 Summer 2002 79 AN EXAMPLE (con’.t) Lift unsaturated air to saturation

80. ATM OCN 100 Summer 2002 80 AN EXAMPLE (con’.t) Lift saturated air to top

81. ATM OCN 100 Summer 2002 81 AN EXAMPLE (con’.t) Force air to sink

82. ATM OCN 100 Summer 2002 82 Announcements u Homework 3 is: –Due NLT 11 AM tomorrow in my mailbox on 8 th Floor of 1225 W. Dayton St.

83. ATM OCN 100 Summer 2002 83 In Reality u Clouds u Vegetation on upwind vs. downwind slopes u Special extreme examples –Chinook Winds –Santa Ana Winds where…

84. ATM OCN 100 Summer 2002 84 Mountain Wave Clouds

85. ATM OCN 100 Summer 2002 85 IR Enhanced Satellite 23 Oct 2001 7AM PDT Clouds

86. ATM OCN 100 Summer 2002 86 Mountains Affect Climate

87. ATM OCN 100 Summer 2002 87 Forest vegetation on West Slopes of Sierras (in Yosemite N.P., CA) Forest vegetation on West Slopes of Sierras (in Yosemite N.P., CA)

88. ATM OCN 100 Summer 2002 88 Arid Vegetation on East Slopes of Sierras (Owens Valley near Bishop, CA)

89. ATM OCN 100 Summer 2002 89 A Day out West Chinook Santa Ana

90. ATM OCN 100 Summer 2002 90 Chinook Winds

91. ATM OCN 100 Summer 2002 91 Santa Ana Winds

92. ATM OCN 100 Summer 2002 92 Effect of moisture on Stability u Recall Stability vs. Instability Criteria for a dry air parcel ….

93. ATM OCN 100 Summer 2002 93 STABLE CONDITIONS Compare Environment with DALR Colder parcel sinks & returns to start Parcel is colder & more dense Environment is warmer & less dense

94. ATM OCN 100 Summer 2002 94 UNSTABLE CONDITIONS Compare Environment with DALR Warmer parcel continues upward Parcel is warmer & less dense Environment is colder & more dense

95. ATM OCN 100 Summer 2002 95 Effect of moisture on Stability u Recall Stability vs. Instability Criteria for a dry air parcel …. u But now consider water vapor & saturated air …

96. ATM OCN 100 Summer 2002 96 ABSOLUTELY STABLE CONDITIONS Compare Environment with SALR & DALR Colder parcel sinks & returns to start

97. ATM OCN 100 Summer 2002 97 UNSTABLE CONDITIONS Compare Environment with DALR Warmer parcel continues upward

98. ATM OCN 100 Summer 2002 98 ABSOLUTELY UNSTABLE CONDITIONS Compare Environment with SALR & DALR Warmer parcel continues upward

99. ATM OCN 100 Summer 2002 99 If STABLE CONDITIONS for Dry Compare Environment with DALR Colder parcel sinks & returns to start

100. ATM OCN 100 Summer 2002 100 But UNSTABLE CONDITIONS for Humid Compare Environment with SALR Warmer parcel continues upward

101. ATM OCN 100 Summer 2002 101 CONDITIONALLY STABLE CONDITIONS Compare Environment with SALR & DALR

102. ATM OCN 100 Summer 2002 102 Stability Criteria See Fig. 6.14 Moran & Morgan (1997) A.Superadiabatic B.Conditionally Stable, Lapse C.Absolutely Stable, Lapse D.Isothermal E.Inversion

103. ATM OCN 100 Summer 2002 103 F. LOW LEVEL SATURATION PROCESSES & PHENOMENA u Fogs – Definition – Comparison between Fog & Clouds; – Fog Formation Mechanisms F cooling to saturation F addition of moisture – Significance

104. ATM OCN 100 Summer 2002 104 Fog over Sydney Harbor

105. ATM OCN 100 Summer 2002 105 Fog Fog is similar to a stratus cloud except that it touches the ground. It is not, necessarily formed in the same manner.

106. ATM OCN 100 Summer 2002 106 Surface Weather Map from an Autumn AM with Isobars & Fronts

107. ATM OCN 100 Summer 2002 107 IFR – Instrument Flight Rules Red Dots: Ceiling < 1000 ft or Visibility < 3 miles

108. ATM OCN 100 Summer 2002 108 FOGS (con’t.) u Fog Classification Fog types named either – by temperature; or – by formation process. where... where...

109. ATM OCN 100 Summer 2002 109 FOGS (con’t.) u Fog Type Classification by Temperature – WARM FOG contains liquid droplets, esp. T > 0 o C – COLD FOG contains supercooled liquid droplets with T -30 o C) – ICE FOG (or ICE CRYSTAL FOG) contains ice crystals when T < -35 o C

110. ATM OCN 100 Summer 2002 110 FOGS (con’t.) u Fog Type Classification by Formation Process – RADIATION FOG – UPSLOPE FOG (or MOUNTAIN FOG) – ADVECTION FOG – STEAM FOG (or SEA SMOKE) – RAIN FOG – With Following Examples

111. ATM OCN 100 Summer 2002 111 FOGS (con’t.) u Fog Type Classification by Formation Process – How did the fog form? – With Following Examples…

112. ATM OCN 100 Summer 2002 112 Radiation Fog (from The Weather Doctor, K. C. Heidorn, PhD)

113. ATM OCN 100 Summer 2002 113 Radiation Fog Cool air by loss of IR radiation

114. ATM OCN 100 Summer 2002 114 Valley Fog (from The Weather Doctor, K. C. Heidorn, PhD)

115. ATM OCN 100 Summer 2002 115 Radiation Fog ( or Valley Fog) Cool air by IR radiation & cold air drainage

116. ATM OCN 100 Summer 2002 116 Upslope Fog (from The Weather Doctor, K. C. Heidorn, PhD)

117. ATM OCN 100 Summer 2002 117 Upslope (or Mountain Fog) Cool air by expansion through lifting

118. ATM OCN 100 Summer 2002 118 Advection Fog (from The Weather Doctor, K. C. Heidorn, PhD)

119. ATM OCN 100 Summer 2002 119 Advection Fog Cool air by transport & contact with cold surface

120. ATM OCN 100 Summer 2002 120 Steam Fog ( or Sea Smoke) Evaporation & saturation of air

121. ATM OCN 100 Summer 2002 121 Steam & Radiation Fog Cooling along with evaporation to saturate air

122. ATM OCN 100 Summer 2002 122 Rain Fog (from The Weather Doctor, K. C. Heidorn, PhD)

123. ATM OCN 100 Summer 2002 123 Rain Fog Evaporation from falling rain

124. ATM OCN 100 Summer 2002 124 FOGS (con’t.) u Fog Type Classification by Formation Process – RADIATION FOG – UPSLOPE FOG (or MOUNTAIN FOG) – ADVECTION FOG – STEAM FOG (or SEA SMOKE) – RAIN FOG

125. ATM OCN 100 Summer 2002 125 FOGS (con’t.) u Fog Type Classification by Formation Process – RADIATION FOG – UPSLOPE FOG (or MOUNTAIN FOG) – ADVECTION FOG – STEAM FOG (or SEA SMOKE) – RAIN FOG – With Following Examples