weather theory part ii (group c)
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Weather Theory Part II (Group C)TRANSCRIPT
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Weather TheoryPart II: Air Movement
Group C: Second Year
PHAK Chapter 11, pages 7-12
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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 lessthick
hypoxia
more
equilibriumheating
nitrogen 21
Coriolis effect right
mercurydecrease
increases
altitudes
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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?
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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
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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.
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Favorable Winds
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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
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Releases heat Retains heat
updraft downdraft
Convective Turbulence
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Intended Flight Path
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Sea and Land Breeze Circulation
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Mountain Turbulence
• Air flows smoothly up mountain but follows contour of terrain back down, forcing airplane down the side
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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
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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
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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
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Microburst (cont’d)
• Difficult to detect
• Low-Level Wind Shear Alert System (LLWAS)
• Can affect any pilot in any airplane
• Undetected, silent danger
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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
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Surface Weather Map
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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
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