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)

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