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. Concerns of Balloonists
The Weather
The Terrain (or Surface)

4. Quiz
Ballooning (Fair) Weather is associated with High or Low Pressure?
Which way do winds blow around: High pressure?
Low pressure?

7. WIND
What is Wind?
Why the wind?
Review of basic concepts

8. ASOS Wind Instruments Wind Vane (left) & Cup Anemometer (right)

9. Aerovane Measures wind speed & direction

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

11. BEAUFORT WIND FORCE SCALE (con’t.)

12. The wind responds to a Difference in air pressure

13. BASIC CONCEPTS Air Pressure (con’t.)

14. Explaining Differences in Air Pressure
Low Pressure
High Pressure

15. Display of Pressure Differences on a Weather Map - Isobars

16. Isobars - - lines of equal barometric pressure - use sea level corrected pressure

17. AIR PRESSURE in the Vertical (con’t.)

18. As a Sidebar… Altimetry
Since pressure decreases at a “reasonably” known rate of mb decrease per 10 meter rise or 0.01 inch of Hg per 10 feet,
then… pressure altimeters are barometers made to read in altitude.
But...

19. Pressure Change with height depends upon Temperature of column - (It is really the density!)

20. WHY THE WIND? (con’t.) Reasons for Atmospheric Motions:
Buoyancy Effects or Dynamic Effects

22. Daily Heating
Heat Gain
Heat Loss
Daylight
Nighttime

23. January Temperatures - Madison, WI (1981-90)
Nighttime
Daylight
Nighttime

24. January Wind Speeds - Madison, WI (1981-90)
Nighttime
Daylight
Nighttime

25. July Temperatures - Madison, WI (1981-90)
Daylight
Nighttime
Nighttime

26. July Wind Speeds - Madison, WI (1981-90)
Daylight
Nighttime
Nighttime

27. ENERGY TRANSPORT: CONVECTION

28. LAPSE CONDITIONS Temperature decreases with height

29. ISOTHERMAL CONDITIONS Temperature remains constant with height

30. INVERSION CONDITIONS Temperature increases with height

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

33. WHY THE WIND? (con’t.) Reasons for Atmospheric Motions:
Buoyancy Effects or Dynamic Effects

34. Air Converging Aloft

36. Air Diverging Aloft

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

39. Boundary Layer Where we live
Extends from surface to approximately 3000 ft. (1000 m)
Consists of
Surface Boundary Layer (30 to 60 ft. & includes Anemometer Level)
Ekman or Spiral Layer (above 60 ft. to Free Atmosphere)

40. Relative Surface Roughness Source: Stull, 1995

41. B. EXPLANATIONS of ATMOSPHERIC MOTION
Practical Problems
Historical Concepts
Forces of Motion & Newton's Laws

42. An example of an equation of motion NASA

43. PRESSURE GRADIENT FORCE

44. PRESSURE GRADIENT FORCE (con’t.)

45. ASSUMPTIONS
For convenience, assume that:
Winds are nearly horizontal;
Atmosphere is in nearly “hydrostatic balance” i.e., air parcels do not accelerate upward or downward;

46. HYDROSTATIC BALANCE CONCEPT See Fig. 9.11 Moran & Morgan (1997)

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

48. HORIZONTAL PRESSURE GRADIENT FORCE (con’t. ) See Fig. 9
HORIZONTAL PRESSURE GRADIENT FORCE (con’t.) See Fig. 9.1 Moran & Morgan (1997) Magnitude depends on isobar spacing!

49. LOCAL WINDS FLOW RESPONDING TO PRESSURE GRADIENT FORCE - LOCAL WINDS
Assumptions:
Only Pressure gradient force operates;
Results from temperature differences
Acts for short time & short distances.
Examples:
Sea-Land Breeze Circulation
Mountain-Valley Breeze Circulation
City-Country Circulation

50. Sea (Lake) Breeze (Graphics from UIUC WW2010)

51. VERTICAL PRESSURE GRADIENTS - Dependency on density (temperature)

52. Sea (Lake) Breeze (con’t.)

53. Sea (Lake) Breeze (con’t.)

54. Sea (Lake) Breeze (con’t.)

55. Sea (Lake) Breeze (con’t.)

56. Sea (Lake) Breeze (con’t.)

57. Sea (Lake) Breeze (con’t.)

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

59. Land Breeze

60. Land Breeze (con’t.)

61. Land Breeze (con’t.)

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

63. Mountain Breeze See Fig. 12.14 Moran & Morgan (1997)

64. Valley Breeze See Fig. 12.14 Moran & Morgan (1997)

65. Larger Scale Flow
Observation:

66. Right with Height

67. PRESSURE GRADIENT FORCE

68. Reason for the Problem Because the earth turns:

69. CORIOLIS EFFECT or FORCE (con’t.)

71. Geostrophic Adjustment

72. Geostrophic Wind See Fig. 9.12 Moran & Morgan (1997)

73. Flow in Friction Layer

74. Variation of Friction Effects with Height

75. Right with Height

76. Varying effects of Surface Roughness

78. Curved Flow

79. Features in a Surface Low (Convergence & Ascent)

80. Features in a Surface High (Sinking & Divergence)

81. Numerical Weather Prediction

82. Numerical Weather Prediction

83. Numerical Weather Prediction

84. My office: Dept. of Atmospheric & Oceanic Sciences hopkins@meteor.wisc.edu

87. UNSTABLE CONDITIONS Compare Environment with DALR Warmer parcel continues upward