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MADISON’S CURRENT WEATHER

Get the latest weather update for Madison at 1000 AM CDT on July 18, 2002. The temperature is 80°F with a dew point of 69°F, relative humidity of 69%, and wind speed of 6 MPH. Stay informed with this updated weather report.

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MADISON’S CURRENT WEATHER

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  1. MADISON’S CURRENT WEATHER Madison Weather at 1000 AM CDT 18 JUL 2002 Updated twice an hour at :05 and :25 Sky/Weather: MOSUNNY Temperature: 80 F (26 C) Dew Point: 69 F (20 C) Relative Humidity: 69% Wind: W6 MPH Barometer: 29.98S (1015.2 mb)

  2. Last 24 hrs in Madison FOG

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

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

  5. Current Dewpoints (oF)

  6. Tomorrow AM Forecast Map

  7. D. BUILDING A RAINDROP (con’t.) • Need to add water to increase cloud droplet size to raindrop size • But… amount needed is proportional to cube of radius • Factors opposing Precipitation • Cloud-producing updrafts greater than droplet’s terminal velocity; • Dry atmosphere below cloud base may evaporate droplet to form VIRGA.where ...

  8. D. BUILDING A RAINDROP (con’t.) • Terminal velocity • Dependent upon size • Amount of water needed depends upon: • Volume of spherical droplet; • or equivalently, the cube of the radius (Since V = 4/3 r3, where r = radius).

  9. D. BUILDING A RAINDROP (con’t.) • So if rcloud = 20 m, an increase to rrain = 200 m: • then a tenfold increase in radius (200 mVs. 20 m)causes a Volume increase that would be 103 = 1000 times larger.

  10. D. BUILDING A RAINDROP (con’t.) • Factors opposing Precipitation • Cloud-producing updrafts greater than droplet’s terminal velocity; • Dry atmosphere below cloud base may evaporate droplet to form VIRGA.

  11. Virga

  12. A Convective Rainshower

  13. E. POSSIBLE PRECIPITATION MECHANISMS (Growth of Liquid rain drops) • The current proposed mechanisms: • Simple Condensation by Diffusion Process • The Collision - Coalescence Process • The Ice Crystal or Bergeron-Findeisen Process or specifically, ...

  14. PRECIPITATION MECHANISM:CONDENSATION-DIFFUSION PROCESS • Based upon H20 vapor molecules condensing upon cloud droplets; • Competing Effects • Curvature Effect • Solute Effect • Condensation needs to overcome surface tension of droplet; • Process would take 24 to 48 hours; • Hence, process is too slow!

  15. PRECIPITATION MECHANISM:COLLISION-COALESCENCE PROCESS • Requires droplets of various sizes, with some greater than 20 m diameter; • Large droplets have greater fall speed; Figure 8.2 Moran & Morgan (1997)

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

  17. PRECIPITATION MECHANISM:ICE CRYSTAL (or Bergeron-Findeisen) PROCESS • Requires a mixture of ice crystals and supercooled liquid droplets; • supercooled droplet remains a liquid at -40oC (-40oF) < T < 0oC (32oF); • smaller droplets are more frequently supercooled.

  18. Saturation Vapor Pressure as a Function of Temperature See Fig. 6.3 Moran & Morgan, 1997

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

  20. F. PRECIPITATION TYPES • Distinguishing Features of Precipitation Types • Liquid (Rain, Drizzle) • Frozen (Snow, Ice Pellets, Hail) • Freezing (Freezing Rain, Freezing Drizzle) where --

  21. LIQUID PRECIPITATIONNational Weather Service

  22. FROZEN PRECIPITATIONNational Weather Service

  23. Snow

  24. RecallPHYSICAL PHASES of H2O • Solid (Ice) -- Note Hexagonal (6 sided) Structure

  25. Varieties of Snowflakes

  26. Varieties of SnowflakesSee Fig. 8.6, Moran & Morgan, 1997

  27. FREEZING PRECIPITATIONNational Weather Service

  28. Freezing Rain

  29. Freezing Rain/Ice Storm

  30. Hail Stones

  31. Hail Stones

  32. Hail Storm

  33. Snow Event

  34. Rain Event

  35. Freezing Rain Event

  36. Ice Pellet (Sleet) Formation

  37. Summary of Precipitation Type Formation

  38. Freezing Rain Climatology

  39. G. PRECIPITATION CLIMATOLOGY - Annual

  40. H. WEATHER MODIFICATION BACKGROUND • Statement of Problem • Why no precipitation? • Can humans cause rain? • For precipitation, need: • sufficient atmospheric humidity; • a cloud; • sufficiently large raindrops/snowflakes to fall & reach ground as rain or snow.

  41. INTENTIONAL ARTIFICIAL WEATHER MODIFICATION • Goals • Stimulate Precipitation • Dissipate Clouds & Fog • Suppress Hail • Modify Hurricanes

  42. C. WEATHER MODIFICATION (con’t.) • Precipitation Stimulation Techniques - "Cloud seeding" • Early Weather Modification Techniques • Modern Precipitation Stimulation Strategies • Problems • Scientific • Legal

  43. TYPICAL STRATEGIES • WARM CLOUDS • Add large hygroscopic nuclei. • COLD CLOUDS • Freeze all supercooled droplets with Dry Ice (Solid CO2); • Add freezing nuclei with ice-like crystal structure with Silver Iodide (AgI).

  44. ATM OCN 100 - Summer 2002 LECTURE 16 ATMOSPHERIC OPTICAL PHENOMENA A. INTRODUCTION • Definition & Scope • Historical Background

  45. B. NATURE OF VISIBLE LIGHT • The Electromagnetic Spectrum • A review

  46. B. NATURE OF VISIBLE LIGHT(con’t.) • Visible Light, Sunlight & the Electromagnetic Spectrum • I. Newton, sunlight & polychromatic light • Visible Light, Color & Human Visual Perception

  47. C. OPTICAL PROCESSES • Optical Phenomena depends upon Processes affecting sunlight • Review of Optical Processes • Scattering • Reflection • Refraction • Dispersion • Diffractionwhere ...

  48. SCATTERING • Redirection of light ray due to suspended particles. • New direction may be in forward or backward direction. • Depends upon relative size of scatterer: • Rayleigh Scatter [small particles] • Mie Scatter [large particles]

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