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A 89 - 100 AB 85 - 88 B 75 - 84 BC 69 - 74 C 51 - 68 D 40 - 50 F < 39

A 89 - 100 AB 85 - 88 B 75 - 84 BC 69 - 74 C 51 - 68 D 40 - 50 F < 39. Mean = 70. MADISON’S CURRENT WEATHER. Madison Weather at 1000 AM CDT 30 JUL 2002 Updated twice an hour at :05 and :25

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A 89 - 100 AB 85 - 88 B 75 - 84 BC 69 - 74 C 51 - 68 D 40 - 50 F < 39

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  1. A 89 - 100 AB 85 - 88 B 75 - 84 BC 69 - 74 C 51 - 68 D 40 - 50 F < 39 Mean = 70

  2. MADISON’S CURRENT WEATHER Madison Weather at 1000 AM CDT 30 JUL 2002 Updated twice an hour at :05 and :25 Sky/Weather: SUNNY Temperature: 80 F (26 C) Dew Point: 69 F (20 C) Relative Humidity: 69% Wind: SW8 MPH Barometer: 30.00F (1015.9 mb)

  3. Last 24 hrs in Madison FOG

  4. CURRENT VISIBLE

  5. Current Surface Weather Map with Isobars (“iso” = equal & “bar” = weight), Fronts and Radar Tight Isobar Packing

  6. Current Surface Winds with Streamlines & Isotachs (“iso” = equal & “tach” = speed) L H L L L L H L H L H L Strong winds withTight Isobar Packing H L L L H H H H

  7. Current Temperatures (°F) & Isotherms(“iso” = equal +”therm” = temperature)

  8. Current Dewpoints (oF)

  9. Tomorrow AM Forecast Map

  10. Announcements • 2nd Hour Exam has been returned. • See exam statistics on http://www.aos.wisc.edu/~hopkins/aos100/exams • Homework #4 also has been returned. Answer Key is posted athttp://www.aos.wisc.edu/~hopkins/aos100/homework • If you have ??, please see me.

  11. ATM OCN 100 - Spring 2002 LECTURE 20 (con’t.) THE THEORY OF WINDS: PART III - RESULTANT ATMOSPHERIC MOTIONS (con’t.) • Introduction & Assumptions Buys-Ballot Law

  12. Buys Ballot Rule

  13. Current Midwest Weather Plot

  14. Current Midwest Weather Analysis L H

  15. Goal • Attempt to develop simple models to explain atmospheric motions appearing on surface weather maps

  16. ASSUMPTIONS For convenience, assume that: • Define motion in terms of horizontal & vertical components. • Rationale: • Winds are nearly horizontal; • Vertical motions typically much smaller. • Make assumptions about the balance of forces:

  17. Summary of Forces for selected modelsSee Table 9.1 Moran & Morgan (1997) MODELS

  18. B. HORIZONTAL EQUATION OF ATMOSPHERIC MOTION • 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.

  19. HYDROSTATIC BALANCE CONCEPT • A Fundamental Assumption: • Earth’s atmosphere remains and is essentially in “hydrostatic balance”. • The Model – • This balance is between the vertically oriented vector quantities: • gravity, & • acceleration due to vertical component of pressure gradient force.

  20. Concept of Hydrostatic BalanceFig. 9.11 Moran & Morgan (1997)

  21. Components in Hydrostatic Balance ModelFig. 9.11 Moran & Morgan (1997) Gravity Vector Direction:“Down” toward Earth center Gravity Vector Magnitude:Decreases with altitude... But  9.8 m/s2or 32 ft/s2

  22. Components in Hydrostatic Balance ModelFig. 9.11 Moran & Morgan (1997) Vert. Press. Grad. Force Vector Direction:“Up” from High to Low Pressure Vert. Press. Grad. Force Vector Magnitude:Depends upon Vert. Pressure Grad. & Density Gravity Vector Direction:“Down” toward Earth center Gravity Vector Magnitude:Decreases with altitude... But  9.8 m/s2or 32 ft/s2

  23. Summary of Forces for selected modelsSee Table 9.1 Moran & Morgan (1997) MODELS

  24. HYDROSTATIC BALANCE CONCEPT (con’t.) • As a result • The atmosphere is maintained; • Convection is somewhat limited.

  25. HORIZONTAL PRESSURE GRADIENT FORCE Horiz. Press. Grad. Force Vector Direction:HightoLow & Perpendicular to theIsobars!

  26. HORIZONTAL PRESSURE GRADIENT FORCE(con’t.)See Fig. 9.1 Moran & Morgan (1997) Magnitude of Pressure Gradient depends on isobar spacing!

  27. As a Result of the HORIZONTAL PRESSURE GRADIENT FORCE (con’t.) Horiz. Press. Grad. Force Vector Magnitude:Depends upon Horiz. Pressure Gradient (i.e., isobar spacing)

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

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

  30. Sea-Land Breeze Circulation RegimeFigure 12.2 Moran & Morgan (1997)

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

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

  33. Sea (Lake) Breeze(con’t.)

  34. Sea (Lake) Breeze(con’t.)

  35. Sea (Lake) Breeze(con’t.)

  36. Sea (Lake) Breeze(con’t.)

  37. Sea (Lake) Breeze(con’t.)

  38. Sea (Lake) Breeze(con’t.) (Lake)

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

  40. Lake Breeze Circulation over Lake MichiganFigure 12.3 Moran & Morgan (1997)

  41. Edge of lake breeze on southern Lake MichiganModis 21 May 2002

  42. Land Breeze

  43. Land Breeze(con’t.)

  44. Land Breeze(con’t.)

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

  46. Mountain BreezeSee Fig. 12.14 Moran & Morgan (1997)

  47. Valley BreezeSee Fig. 12.14 Moran & Morgan (1997)

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

  49. Summary of Forces for selected modelsSee Table 9.1 Moran & Morgan (1997) MODELS

  50. “GEOSTROPHIC FLOW” (con’t.)Assumptions Straight isobars Parallel isobars No friction Horizontal flow

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