Turbulence Flashcards
Reporting turbulence x3
Light - no difficulty walking-slight changes 5-10kts
Moderate - positive control still/walking difficult - 15/25kt
Severe - abrupt out of control/walking impossible - 25kt+
Thermal Turbulence
Over land in late afternoon
Cumulus clouds
Mechanical turbulence
Frictional surface causes disruption in flow
Light winds + smooth surface less turbulent
Mountain waves turbulence
Form if there is stability on lee side
Requires strong winds 30 degrees to mountain range
Wind speed 20kt on ridge
Effects up to x3 mountain height
Extends downwind 50-100 miles
Mountain waves vertical speed
600ft per min
Cap clouds
Formed by air being pushed over mountain
Lenticular clouds
Below osscilations could be indication of turbulence
Mountain wave management tips
Overly at 90 degree to mountain
Fly as high as possible
Avoid flying on leeward side
Pre flight briefing
CAT Turbulence in Jet streams
Worst CAT will be on cold air side of jets core
Second worse just above core
How is low level wind shear reported
Pilot reports
Low level wind shear alerting system
ATC/METAR (WS27R for example)
Horizontal wind shear
Change in wind speed at same level
Vertical wind shear
Change in direction or speed in climb or descent
Wind shear causes
Frontal passage
Microburst
Thunderstorms
Wind Shear - Friction Layer
Mechanical and thermal turbulence in friction layer
Smooth laminar flow above
Wind shear - sea/land breeze
Onshore breeze blowing at different direction to inland winds
What level is low level wind shear defined as
1600ft - 500m aal
Rotor Zone
Hazard associated with MTW
Lies level with the mountain ride
Most power fuel rotor lies beneath the first wave crest on the lee side of range
Conditions needed for mountain waves
High wind speed of 15-20kt
Wind direction must be 30 degrees perpendicular to range
Region of marked stability at mountain top
Less stable air above and below
Low level wind shear is up to
1600ft
Definition of turbulence
Abrupt change in airflow caused by vortices of different sizes.
SEV MTW on SIGMET meaning
Downwards of 600ft or more
How often should windshread alert systems be updated
Every minute
What factors increase the friction layer
Roughness of the terrain - greater roughness greater the mixing and strength of vertical deflection
Wind speed - higher speed more mixing and deflection
Stability of air - instability more mixing
Time of day - warm afternoons thermal convection more mixing
