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Weather Theory Part II (Group C)
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Weather Theory Part II (Group C)

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Weather Theory Part II (Group C)

Weather Theory Part II (Group C)

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  • 1. Weather Theory Part II: Air Movement Group C: Second Year PHAK Chapter 11, pages 7-12
  • 2. Recall
    • Air always strives to achieve _________ due to unequal _______ of Earth’s surface
    • Atmosphere is 78% ________, __% oxygen, and 1% other gases
    • Warm air is ____ (____ dense), thus rises while cool air is _____ (____ dense), thus sinks
    • ____________ deflects air to the ____ in the Northern Hemisphere
    • Air is measured in inches of ________
    • Pressure and temperature ________ as altitude ________
    • Lower pressure causes longer takeoff roll
    • Lower oxygen concentration at higher _______ can/will cause _______
    thin less thick hypoxia more equilibrium heating nitrogen 21 Coriolis effect right mercury decrease increases altitudes
  • 3. Essential Questions
    • What is the difference between wind and currents?
    • What is the difference between cyclonic and anti-cyclonic circulation?
    • What effects do surfaces have that retain heat? Release heat?
    • What is low-level wind shear and what sorts of hazards does it present?
    • How can wind and pressure be depicted on a surface weather map?
  • 4. Wind and Currents
    • Air always strives equilibrium – air moves from high pressure to low pressure
    • Currents – vertical movement of air
    • Wind – horizontal movement of air
  • 5. Wind Patterns
    • Vertical movements – currents
    • Horizontal movements – winds
    • Anti-cyclonic circulation is clockwise movement of air around an area of high pressure
    • Cyclonic circulation is counterclockwise movement of air around an area of low pressure
    • High pressure:
      • Dry, stable, descending
      • Good weather 
    • Low pressure:
      • Unstable, cloudiness and precipitation
      • Bad weather 
    • Favorable winds
    • Large-scale only; doesn’t account for local conditions, geographical abnormalities, etc.
  • 6. Favorable Winds
  • 7. Convective Currents
    • Releases heat:
      • Plowed ground
      • Rocks
      • Sand
    • Retains heat:
      • Water
      • Trees
    • Convective currents cause turbulent air when flying low, in warm weather, or over varying surfaces
  • 8. Releases heat Retains heat updraft downdraft Convective Turbulence
  • 9. Intended Flight Path
  • 10. Sea and Land Breeze Circulation
  • 11. Mountain Turbulence
    • Air flows smoothly up mountain but follows contour of terrain back down, forcing airplane down the side
  • 12. Low-Level Wind Shear
    • Sudden, drastic change in wind speed and/or direction over a very small area
    • Violent updrafts and downdrafts
    • Abrupt changes to horizontal movement of aircraft
    • Hazardous due to close proximity of aircraft close to ground
    • Directional wind changes of 180 and speed changes of 50+ knots associated
  • 13. Low-Level Wind Shear (cont’d)
    • Rapid changes in wind direction and velocity change the wind’s relation to the aircraft, disrupting the normal flight attitude and performance of the aircraft
    • Most severe type associated with convective precipitation or rain from thunderstorms
  • 14. Microburst
    • Type of low-level wind shear
    • Associated with convective precipiration
    • Normally >1 mile horizontal & ≥1,000 feet vertically and lasts 15 minutes, during which can produce downdrafts of up to 6,000 fpm
    • Microburst behavior:
      • 1. performance-increasing headwind
      • 2. performance-decreasing downdraft
      • 3. rapid tailwind shear
      • 4. can result in terrain impact or flight dangerously close to the ground
  • 15.  
  • 16.  
  • 17. Microburst (cont’d)
    • Difficult to detect
    • Low-Level Wind Shear Alert System (LLWAS)
    • Can affect any pilot in any airplane
    • Undetected, silent danger
  • 18. Wind on Surface Weather Maps
    • Information about fronts, areas of high/low pressure, surface winds
    • How to read:
      • Circle indicates weather station
      • No line (two circles) represents calm wind
      • Direction of line indicates wind direction
      • Half-barb represents 5 knots
      • Full barb represents 10 knots
      • Pennant represents 50 knots
  • 19.  
  • 20. Surface Weather Map
  • 21. Isobars
    • Lines drawn on the chart to depict areas of equal pressure
    • Reveals pressure gradient or change in pressure over time
    • Close isobars represent steep pressure gradient, strong winds
    • Further isobars represent shallow pressure gradient, light winds
  • 22.  

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