Jet Stream Overview Clear Air Turbulence Risk Mitigation Strategies

1. REV02_221114
Keep It Simple Series
Risk Mitigation
Capt. RHW
JET STREAM Overview
JET STREAM CAT CAT Risk Mitigation YouTube References
CAT Risk Mitigation Strategies

2. JET STREAM
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3. JET STREAM Overview (1/3)
Introduction
• A Jet stream is narrow, fast moving current of air,
normally close to the Tropopause
• Westerly wind, but the flow often meanders southward
and northward
• Jet streams follow the boundaries between hot and
cold air. Jet streams are the strongest in winters
Characteristic
• Wind speed greater than 60 kt
• Persist from 30 minutes to 1 day.
• Dimensions
• 100 to 300 miles long
• 50 to 100 miles wide
• 5,000 feet deep.
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4. JET STREAM Overview (2/3)
Common Jet Stream
Latitude
Polar Jet Stream 70˚ to 80˚ N/S
Polar front Jet Stream 45˚ to 65˚ N/S
Sub-tropical Jet Stream 20˚ to 40˚ N/S
Equatorial Jet Stream 10˚ to 15˚ N/S
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5. JET STREAM Overview (3/3)
Polar front Jet Stream
• Between 40˚N and 65˚N and at around 50˚S.
• Jet Stream follows on the Polar Front
• A zig-zag shape which is westerly on average.
• Tending die out a bit in summer
Sub-tropical Jet Stream
• In winter : Between 25˚ to 40˚N/S
• In summer : Between 40˚ to 45˚N/S
• Constant westerly direction
• Exist all year round
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6. CAT
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7. CAT Overview(1/2)
Introduction
• Sudden severe turbulence occurring in cloudless
regions
• High-altitude turbulence encountered outside of
convective clouds
• The windshear within and around jet streams leads to
friction
Characteristic
• Turbulence in cirrus clouds
• Vicinity of jet streams, standing lenticular clouds,
thunderstorms
• Unexpectedly and frequently without visual clues
• Moderate CAT when vertical wind shear is 5kts per
1,000ft or greater, and/or horizontal wind shear is
40kts per 150 miles or greater.
Intensity
• Primary CAT Area (①) : Level with the core of the jet
on the cold air side.
• Secondary CAT Area (②) : Above the core, Above the
warm air tropopause
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Cold side
Jet Core Level
Warm air Tropopause
Above Core

8. Identification
CAT Overview (2/2)
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9. CAT Risk Mitigation
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10. Defences
• Flight Planning
SIGMET charts display the forecast location and strength of Jet Streams, the level of the Tropopause and areas of CAT.
Significant weather charts also show Jet Streams, Fronts, and area of CB, icing and turbulence forecasted.
• Airmanship
A rapid change in OAT indicates passage from one air mass to another, and if the aircraft is close to the Tropopause
this can indicate the likely presence of Jet Stream.
CAT Risk Mitigation Strategies (1/3)
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11. CAT Risk Mitigation Strategies (2/3)
Decide High Possibility of CAT
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12. Solution
• Slow down
• Notify the crew/illuminate seat belt sign
• Switch on Engine Ignition
• Inform ATC.
• Notify ATC/warn other aircraft.
• Fly to lower possibility Area
• Try flying 2,000ft and 4,000ft lower. (Climb is not always correct in turbulent air)
• Seek information from aircraft ahead and consider adjusting your route.
• Assess Damage/Injuries
CAT Risk Mitigation Strategies (3/3)
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13. YouTube Movie Clip
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https://youtu.be/hNHcF0ASv0w https://youtu.be/GUYboL86HEM

14. References
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