1. Hot Airventure 1 Weather 101 and beyond Edward J. Hopkins Dept. of Atmospheric & Oceanic Sciences Univ. of Wisconsin-Madison Midwest Hot Air Balloon Safety Seminar “Hot Aireventure” Oshkosh 3 March 2001

2. Hot Airventure 2 Boundary Layer F Where we live F Extends from surface to ?

3. Hot Airventure 3 Concerns of Balloonists F The Winds F The Surface

4. Hot Airventure 4 WIND F Why Winds? –Local Thermal Effects –Large Scale Dynamic Effects

5. Hot Airventure 5 High Pressure Systems F Circulation F Consequences F Types

6. Hot Airventure 6 The Surface F The “Obvious” –Obstacles to take-off and landing (e.g., trees, power lines, animals) F The Surface and the Winds –Affects the Boundary Layer wind flow –Can produce local wind regimes

7. Hot Airventure 7 Relative Surface Roughness

8. Hot Airventure 8

9. 9 Quiz F Which way do winds blow around: High Low

10. Hot Airventure 10 Features in a Surface Low (Convergence & Ascent)

11. Hot Airventure 11 Features in a Surface High (Sinking & Divergence)

12. Hot Airventure 12 January Temperatures - Madison, WI (1981-90)

13. Hot Airventure 13 January Wind Speeds - Madison, WI (1981-90)

14. Hot Airventure 14 July Temperatures - Madison, WI (1981-90)

15. Hot Airventure 15 July Wind Speeds - Madison, WI (1981-90)

16. Hot Airventure 16 Daily Heating

17. Hot Airventure 17

18. Hot Airventure 18

19. Hot Airventure 19

20. Hot Airventure 20 U.S. STANDARD ATMOSPHERE See Fig. 1.9 Moran & Morgan (1997) Troposphere Stratosphere Mesosphere Thermosphere Tropopause Stratopause Mesopause

21. Hot Airventure 21 Weather Satellites and the Space Science & Engineering Center

22. Hot Airventure 22 BASIC CONCEPTS Air Pressure (con’t.)

23. Hot Airventure 23 Explaining Differences in Air Pressure F Low Pressure F High Pressure

24. Hot Airventure 24 Display of Pressure Differences on a Weather Map - Isobars

25. Hot Airventure 25 AIR PRESSURE CLIMATOLOGY (con’t.)

26. Hot Airventure 26 AIR PRESSURE CLIMATOLOGY (con’t.)

27. Hot Airventure 27 AIR PRESSURE CLIMATOLOGY (con’t.) 50% of surface

28. Hot Airventure 28 D. VARIATION OF OBSERVED AIR TEMPERATURE WITH HEIGHT F Temperature lapse rates – Rate of cooling with height – Units: degrees per meter or feet or kilometers F Layer nomenclature – lapse – inversion – isothermal where...

29. Hot Airventure 29 LAPSE CONDITIONS Temperature decreases with height

30. Hot Airventure 30 INVERSION CONDITIONS Temperature increases with height

31. Hot Airventure 31 ISOTHERMAL CONDITIONS Temperature remains constant with height

32. Hot Airventure 32 ENERGY TRANSPORT: CONVECTION (con’t.)

33. Hot Airventure 33 UNSTABLE CONDITIONS Compare Environment with DALR Warmer parcel continues upward

34. Hot Airventure 34 BEAUFORT WIND FORCE SCALE [Modern version, Source: Federal Meteorological Handbook I]

35. Hot Airventure 35 BEAUFORT WIND FORCE SCALE (con’t.)

36. Hot Airventure 36 ASOS Wind Instruments Wind Vane (left) & Cup Anemometer (right)

37. Hot Airventure 37 Aerovane Measures wind speed & direction

38. Hot Airventure 38 B. EXPLANATIONS of ATMOSPHERIC MOTION F Practical Problems F Historical Concepts F Forces of Motion & Newton's Laws

39. Hot Airventure 39 C. DESCRIBING ATMOSPHERIC MOTION F Reasons for Atmospheric Motions: –Buoyancy Effects or Dynamic Effects

40. Hot Airventure 40 C. DESCRIBING ATMOSPHERIC MOTION F Complications involved with Atmospheric Motion: –Spherical planet; –Rotating planet & non-inertial frame of reference.

41. Hot Airventure 41 DESCRIBING ATMOSPHERIC MOTION (con’t.) F Three-Dimensional Equation of Motion for the Atmosphere –A vector equation; –Entails specification of all forces per unit mass (i.e., equivalent to acceleration); –All forces do not act alone; –Vector sum of individual forces equals net force.

42. Hot Airventure 42 Numerical Weather Prediction

43. Hot Airventure 43 Numerical Weather Prediction

44. Hot Airventure 44 Numerical Weather Prediction

45. Hot Airventure 45 An example of an equation of motion NASA

46. Hot Airventure 46 FORCES ASSOCIATED WITH ATMOSPHERIC MOTION F Following forces influence motion of air parcels: –Pressure Gradient Force –Gravitational Force or Gravity –Coriolis Effect or "Force" –Frictional Force or Friction –Centripetal Force or more specifically --

47. Hot Airventure 47 PRESSURE GRADIENT FORCE F Generated by differences in pressure within a fluid element; F Responsible for initiation of all air motion;

48. Hot Airventure 48 PRESSURE GRADIENT FORCE (con’t.) F A 3-dimensional vector that has: F Magnitude of pressure gradient force vector depends: –directly upon difference in pressure over a given distance (i.e., slope or grade equals “pressure gradient”). F Direction of pressure gradient force vector is: –from H igh pressure to L ow pressure, –along steepest direction of pressure gradient.

49. Hot Airventure 49 PRESSURE GRADIENT FORCE (con’t.)

50. Hot Airventure 50 PRESSURE GRADIENT FORCE (con’t.)

51. Hot Airventure 51 GRAVITATIONAL FORCE or GRAVITY F Produced by mutual physical attraction between massive bodies; F Gravity refers to acceleration; F Acts continuously, regardless of motion; F A vector quantity that has: –Direction – toward center of earth. –Magnitude ~ 9.8 m/s 2 (32 ft/s 2 )

52. Hot Airventure 52 GRAVITATIONAL FORCE or GRAVITY (con’t.) F Magnitude of gravity vector depends upon: –Mass of earth & object; –Distance between two objects; (inverse square relationship). – [NOTE: Issac Newton quantified relationship] –Usually gravity is assumed 32 ft/s 2 = 9.8m/s 2. F Direction of gravity vector is –toward vicinity of earth’s center (i.e., essentially downward).

53. Hot Airventure 53 CORIOLIS EFFECT or FORCE F Produced by earth’s rotation; F A “fictitious force” used to explain apparent deflection of moving object on a rotating frame of reference;

54. Hot Airventure 54 CORIOLIS EFFECT or FORCE (con’t.) Speed is dependent upon latitude:

55. Hot Airventure 55 CORIOLIS EFFECT or FORCE (con’t.)

56. Hot Airventure 56 CORIOLIS EFFECT or FORCE (con’t.) F Produced by earth’s rotation; F A “fictitious force” used to explain apparent deflection of moving object on a rotating frame of reference; F Acts only after motion is initiated; F Can only modify direction of motion; F A 3-dimensional vector, but consider only horizontal component described by:

57. Hot Airventure 57 CORIOLIS EFFECT or FORCE (con’t.) F Magnitude of horizontal Coriolis force vector depends upon: –Rotation rate of earth (Direct relationship); –Speed of object; (Direct relationship) –Latitude (specifically, sine of latitude).

58. Hot Airventure 58 CORIOLIS EFFECT or FORCE (con’t.) F Direction of horizontal component of Coriolis force vector: –Causes a deflection of moving object to right of direction of motion in Northern Hemisphere; but –Deflects moving object to left of intended motion in Southern Hemisphere.

59. Hot Airventure 59 FRICTIONAL FORCE or FRICTION F Produced by “viscosity” (interactions of moving fluid elements with one another or with a boundary surface) due to: –random molecular motions; –large random turbulent motions of fluid associated with either: u thermal turbulence u mechanical turbulence

60. Hot Airventure 60 FRICTIONAL FORCE (con’t.) F Acts only after motion is initiated; F Acts to retard motion; F Magnitude of friction force vector depends upon: –Speed of motion of fluid; –Type of surface, e.g., “surface roughness”; –Temperature structure of fluid. F Direction of friction force vector is –opposite motion vector.

61. Hot Airventure 61 CENTRIPETAL FORCE F Produces curved motion; F Opposite the “centrifugal force”; F Acts only after motion is initiated; In reality, a net force Used to describe imbalance of other forces in curved motion;

62. Hot Airventure 62 CENTRIPETAL FORCE VECTOR (con’t.) F Centripetal force vector is described by: F Magnitude of centripetal force vector depends upon: –Speed of instantaneous motion (a direct relationship); –Radius of curvature (an inverse relationship). F Direction of centripetal force vector is –inward toward center of curvature.

63. Hot Airventure 63 SUMMARIZING F A 3-D Equation of Motion for Atmosphere (in word form) : Net force = Pressure gradient force + gravitation force + Coriolis force + friction. F Notes: –The above is a vector equation! –Since a unit mass is used, force is equivalent to an acceleration.

64. Hot Airventure 64 Isobars - - lines of equal barometric pressure - use sea level corrected pressure

65. Hot Airventure 65 Demonstrating Buys -Ballot Rule

66. Hot Airventure 66 Demonstrating Buys -Ballot Rule

67. Hot Airventure 67 BUYS-BALLOT RULE F Empirical relationship stated by Dutch meteorologist Buys-Ballot in 1850’s; F With your back to wind, Low pressure is to your left in Northern Hemisphere; F However, in Southern Hemisphere, Low is to your right ; F Mathematically proved by American meteorologist Wm. Ferrel in 1850’s.

68. Hot Airventure 68 ASSUMPTIONS For convenience, assume that: F Winds are nearly horizontal; F Atmosphere is in nearly “hydrostatic balance” i.e., air parcels do not accelerate upward or downward; F Define motion in terms of horizontal & vertical components.

69. Hot Airventure 69 B. HORIZONTAL EQUATION OF ATMOSPHERIC MOTION F The 3-D vector Equation of Atmospheric Motion can be written in terms of horizontal and vertical components: Net force = Horizontal Pressure gradient force + Vertical Pressure gradient force + gravity + Coriolis force + friction.

70. Hot Airventure 70 HYDROSTATIC BALANCE CONCEPT F Earth’s atmosphere remains and is essentially in “hydrostatic balance”. F This balance is between the vertically oriented vector quantities: –gravity, and –acceleration due to vertical component of pressure gradient force.

71. Hot Airventure 71 HYDROSTATIC BALANCE CONCEPT See Fig. 9.11 Moran & Morgan (1997)

72. Hot Airventure 72 THE VERTICAL PRESSURE GRADIENT FORCE F Magnitude of Vertical Pressure Gradient force vector is: – a function of both air density & vertical component of pressure gradient. F Direction of Vertical Pressure Gradient force is: – always pointed upward, from high pressure (near surface) to low pressure (aloft).

73. Hot Airventure 73 HYDROSTATIC BALANCE CONCEPT (con’t.) F Assume that acceleration of gravity is essentially constant with altitude; F Air pressure ALWAYS decreases with increased altitude in atmosphere; F But, rate of pressure decrease with altitude depends upon density of air column: –Decrease is more rapid in cold, dense air column than in warm, less dense column.

74. Hot Airventure 74 VERTICAL PRESSURE GRADIENTS - Dependency on density (temperature)

75. Hot Airventure 75 VERTICAL PRESSURE GRADIENTS

76. Hot Airventure 76 HYDROSTATIC BALANCE CONCEPT (con’t.)  In summary, acceleration vectors of gravity and vertical pressure gradient are equal in magnitude, but opposite in direction: F Net, V = 0 = F PG,V + g or F PG,V = - g (A vector summation). F A balance exists between these vertically oriented vector quantities, meaning no net vertical force nor acceleration!

77. Hot Airventure 77 THE HORIZONTAL PRESSURE GRADIENT FORCE F Parcels are accelerated in horizontal direction from High to Low pressure. F Direction of force & resulting accelerating motion is perpendicular to isobars on a surface weather map. F Magnitude of acceleration is inversely proportional to isobar spacing. – (i.e., greater horizontal pressure gradient force with tightly packed isobars).

78. Hot Airventure 78 HORIZONTAL PRESSURE GRADIENT FORCE (con’t.) Direction is from High to Low pressure!

79. Hot Airventure 79 HORIZONTAL PRESSURE GRADIENT FORCE (con’t.) See Fig. 9.1 Moran & Morgan (1997) Magnitude depends on isobar spacing!

80. Hot Airventure 80 AS A RESULT - F The 3-D vector Equation of Atmospheric Motion can be rewritten:  Horizontal Component: Net horizontal force = Horizontal Pressure gradient force + + Coriolis force + friction; F Net, H = F PG,H + F Cor + F Friction (A vector summation).

81. Hot Airventure 81 AS A RESULT (con’t.)  Vertical Component: Vertical Pressure gradient force + gravity Since: Net vertical force = 0 = Vertical Pressure gradient force + gravity F PG,V + g = 0. (A vector summation). (a statement of Hydrostatic Balance Assumption ).

82. Hot Airventure 82 Recall VERTICAL PRESSURE GRADIENTS - Dependency on density (temperature)

83. Hot Airventure 83 C. FLOW RESPONDING TO PRESSURE GRADIENT FORCE - LOCAL WINDS F Assumptions: –Only Pressure gradient force operates due to local pressure differences; –Horizontal flow. –  Net force = pressure gradient force F Examples: –Sea-Land Breeze Circulation –Mountain-Valley Breeze Circulation –City-Country Circulation

84. Hot Airventure 84 Sea (Lake) Breeze (Graphics from UIUC WW2010)

85. Hot Airventure 85 REASONS FOR LAND-SEA TEMPERATURE DIFFERENCES F Water has higher heat capacity – Smaller temperature response for heat added F Water is a fluid – Mixing warm water downward F Water is transparent – Sunlight penetrates to depth F Water surface experiences evaporation – Evaporative cooling

86. Hot Airventure 86 Sea (Lake) Breeze (con’t.)

87. Hot Airventure 87 Sea (Lake) Breeze (con’t.)

88. Hot Airventure 88 Sea (Lake) Breeze (con’t.)

89. Hot Airventure 89 Sea (Lake) Breeze (con’t.)

90. Hot Airventure 90 Sea (Lake) Breeze (con’t.)

91. Hot Airventure 91 Sea (Lake) Breeze (con’t.) (Lake)

92. Hot Airventure 92 Sea (Lake) Breeze (con’t.) See Fig. 12.2 A Moran & Morgan (1997)

93. Hot Airventure 93 Land Breeze

94. Hot Airventure 94 Land Breeze (con’t.)

95. Hot Airventure 95 Land Breeze (con’t.)

96. Hot Airventure 96 Land Breeze (con’t.) See Fig. 12.2 B Moran & Morgan (1997)

97. Hot Airventure 97 Mountain Breeze See Fig. 12.14 Moran & Morgan (1997)

98. Hot Airventure 98 Valley Breeze See Fig. 12.14 Moran & Morgan (1997)

99. Hot Airventure 99 D. STRAIGHT-LINE, BALANCED, FRICTIONLESS MOTION - “GEOSTROPHIC FLOW” F A powerful conceptual model involving horizontal motion on rotating planet; F Background & Word Derivation: –Named by Sir Napier Shaw in 1916: “Geo” = earth + “strephein” = to turn.

100. Hot Airventure 100 “GEOSTROPHIC FLOW” (con’t.) F Assumptions –horizontal flow (F PG,V + g = 0); –balanced flow (F Net, H = 0); –no friction (F Friction = 0); –straight line flow (with straight isobars) (F Centripetal = 0); –parallel and equally spaced isobars (F PG,H = constant). F Initiation of Geostrophic Flow

101. Hot Airventure 101 Geostrophic Adjustment See Fig. 9.12 Moran & Morgan (1997)

102. Hot Airventure 102 “GEOSTROPHIC FLOW” (con’t.) F Resultant Geostrophic Flow –Balance between horizontal components of pressure gradient & Coriolis forces, or 0 = F PG,H + F Cor (A vector summation). F Geostrophic Wind vector (V g ) can be described as:

103. Hot Airventure 103 “GEOSTROPHIC FLOW” (con’t.) F Direction of V g vector is: –parallel to isobars, with L ow pressure to left (in Northern Hemisphere); F Magnitude of V g vector is related: –Directly to pressure gradient; –Inversely to Coriolis force (i.e., latitude).

104. Hot Airventure 104 “GEOSTROPHIC FLOW” (con’t.) F Implications of Geostrophic Balance –Geostrophic wind (V g ) is: u a hypothetical wind u a balance between –horizontal pressure gradient (isobar spacing) –latitude (or Coriolis effect) F Dilemma

105. Hot Airventure 105 Geostrophic Wind See Fig. 9.12 Moran & Morgan (1997)

106. Hot Airventure 106 E. BALANCED FLOW in FRICTION LAYER F The Nature of Friction F The Friction Layer F The Effect of Friction upon the Geostrophic Wind F Assumptions –Same as for geostrophic wind case, except F Friction is not zero.

107. Hot Airventure 107 FLOW IN FRICTION LAYER (con’t.) F Resultant Motion 0 = F PG,H + F Cor + F Friction (A vector summation). –Magnitude of flow is less than geostrophic wind. –Direction of flow is turned at angle across isobars toward L ow pressure in either hemisphere.

108. Hot Airventure 108 Flow in Friction Layer See Fig. 9.15 Moran & Morgan (1997)

109. Hot Airventure 109 FLOW IN FRICTION LAYER (con’t.) F Variations of Near-Surface Winds with Height –Wind speeds reach zero at surface & increase to geostrophic at top of friction layer; –Wind direction at lower levels turned more toward L ow, then become parallel to isobars; –The result, a wind spiral is formed.

110. Hot Airventure 110 F. CURVED, HORIZONTAL BALANCED MOTION - “GRADIENT FLOW” F Assumptions –horizontal flow ( F PG,V + g = 0); –no friction (F Friction = 0); –curved flow (with curved isobars) (F Centripetal = F Net, H ); –concentric and equally spaced isobars (F PG,H = constant).

111. Hot Airventure 111 Curved Flow

112. Hot Airventure 112 “GRADIENT FLOW” (con’t.)  Resultant flow without Friction F Centripetal = F PG,H + F Cor (A vector summation). F Two cases: –Cyclonic Flow (around a low pressure cell) –Anticyclonic Flow (around a high pressure cell)

113. Hot Airventure 113 “GRADIENT FLOW” (con’t.) See Moran and Morgan (1997): F Figure 9.14 Cyclonic Flow F Figure 9.13 Anticyclonic Flow

114. Hot Airventure 114 G. GRADIENT FLOW WITH FRICTION  Resultant flow with Friction F Centripetal = F PG,H + F Cor + F Friction (A vector summation). F Applicability to the Atmosphere F Situation F Resultant Diagrams

115. Hot Airventure 115 H. RELATIONSHIPS BETWEEN HORIZONTAL & VERTICAL MOTIONS F Dilemma F Convergence / Divergence F Principle of Mass Continuity

116. Hot Airventure 116 Features in a Surface Low (Convergence & Ascent)

117. Hot Airventure 117 Features in a Surface High (Sinking & Divergence)

118. Hot Airventure 118 VERTICAL PRESSURE GRADIENTS - Dependency on density (temperature)

119. Hot Airventure 119 Recall VERTICAL PRESSURE GRADIENTS - Dependency on density (temperature)

120. Hot Airventure 120