Block 3 - Lesson 3 - Shear Turbulence
What is the critical shear value?
the point at which wave turbulence will turn into eddies
What is a temperature inversion?
An increase of temperature with height in the lower levels of the atmosphere (Caps convective turbulence)
What is wind shear gradient?
Magnitude of shear (Knots/distance)
Where are the probable locations of shear turbulence?
Surface Friction, Kelvin-Helmholtz Waves, Temperature Inversions, Fronts, Jet Streams
What are the two requirements for shear turbulence?
Wind Shear and Stability
How can you use weather information to anticipate possible areas of turbulence caused by surface friction?
Wind speed above 25 knots, strong pressure gradient,
Wha is wind shear?
a change in wind direction and or speed over some distance
what are the characteristics of kelvin-helmholtz waves and their hazards?
forms in crest of mountain waves, shallow layer, moderate to severe turbulence
How can you categorize wind shear experienced with fronts at low altitudes and high altitudes?
low level you have directional shear, high level you have speed shear
what is the slope of a cold front?
1 nm up to 50 nm across (slopes behind the frontal feature)
what frontal temperature gradient produces moderate to severe turbulence?
10 degree per 50nm
What is the slope of a warm front?
1nm up to 200nm across (slopes in front of the frontal feature)
What frontal speed produces moderate to severe turbulence?
30 knots
What conditions produce moderate turbulence in the boundary layer?
30 knots of greater of wind
What is the shear value for moderate turbulence?
5 knots/1000 ft or 40 knots/150nm
Where is the common locations of CAT?
Above jet core (tropical tropopause), north and below jet core
what actions can the pilot take to minimize the effects of shear turbulence caused by terrain induced temperature inversions?
Be alert slow to Va
What conditions produce shear turbulence associated with terrain induced temperature inversions?
Cold air drainage with stronger winds aloft, most common at night and early morning
Calculate final approach speed based on gusts?
Half the gust factor added to FAS
What is the progression of shear turbulence from a wave to eddies?
Laminar flow to waves to eddies
What conditions produce shear turbulence associated with nocturnal radiation inversions?
Low wind, heavier above the inversion, clear calm night. Late at Night and Early Morning
What are the two types of inversions that produce shear turbulence?
Nocturnal Radiation Inversions, Terrain Induced Inversions
what actions should the pilot take to minimize the effects of shear turbulence caused by nocturnal radiation inversions?
Slow to Va and be alert
What factors determine the intensity of turbulence associated with fronts?
Speed of front (greater than 30 - mod/severe turbulence) Temperature gradient (10 degree in 50nm - mod/severe turbulence)
What is the relationship between wind shear and stability?
The more stable the atmosphere the more shear is needed to create turbulence (dikes example)
What conditions influence the depth of the boundary layer?
Time of Year, Time of Day, Wind Speed, Stability, Terrain (Wind speed is most important)
What clouds indicate CAT?
Transverse cirrus bands - Perpendicular to jet stream
What cloud pattern do Kelvin-Helmholtz waves produce?
Waves
Where is the jet stream on constant pressure charts?
areas of wind above 80 knots
Where is a jet streak on constant pressure charts?
areas where there are higher winds
What should pilots do in order to minimize the effects of shear turbulence caused by fronts?
enroute - parallell the front, approach & departure - consider LLWS
What is the boundary layer?
layer in which friction affects the wind
Where are the areas of strong shear on constant pressure charts?
north of the jet streak
Calculate the heigh of a front above the ground based on slope and distance?
take the distance according to the calculations and then figure it out because o the ratio
How can a pilot avoid or minimize the effects of turbulence caused by surface friction?
takeoff at a higher airspeed and climb above the boundary layer, slow to below Va, land at a higher airspeed
How does wind direction and speed change with height?
wind speed increases exponentially to 500ft agl, direction changes very little, above 500ft agl wind speed slowly increases, direction will turn clockwise with height
