Wind Shear ( Lesson #3 )

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Define temperature inversion

An increase in temperature with height`

What are the 2 requirements for wind shear

A change in wind direction and/or speed over some distance

Anticipate possible areas of turbulence caused by surface friction

Where wind speeds are >25kts

How does wind change direction and speed with height

Wind turns clockwise with height

What frontal temperature gradient produces moderate to severe turbulence

10°F in 50 NM

What is the approximate height / distance of a warm front?

1 NM 200 NM Distance

What conditions produce shear turbulence associated with nocturnal radiation inversions

1. Clear Sky 2. High Pressure

What conditions produce shear turbulence associated with terrain induced temperature inversions

1. High pressure system 2. Valley / sloping terrain

What are the two types of temperature inversions that produce shear turbulence

1. Nocturnal Radiation Inversion 2. Terrain Induced Inversion

What factors determine the intensity of turbulence associated with fronts

1. Speed of front 2. Temperature Gradient 3. Terrain

What are the 2 wind speeds and how do they affect the depth of the boundary layer?

1. Strong Wind - Thick Boundary Layer 2. Weak Wind - Shallow Boundary Layer

What are the probable location of shear turbulence

1. Surface Friction 2. Kelvin-Helmholtz Waves 3. Temperature Inversions 4. Fronts 5. Jet Streams

How can a pilot avoid effects of turbulence caused by surface friction

1. Takeoff with higher airspeed 2. Climb above boundary layer

What are common locations of clear air turbulence

1. Upper Fronts 2. Tropopause

Describe the progression of shear turbulence from a wave to Eddie

1. Wind shear induces the wave 2. Wave Break - At critical shear value 3. Leads into eddie turbulence

Calculate the final approach speed of an airplane based on gust factor

16G24KT Gust factor: 24-16 = 8 kts Approach Speed + ½ (Gust Factor)

What is the approximate height / distance of a cold front?

1NM Height 50 NM Distance

What is the shear value for moderate turbulence

5-6 kts per 1,000ft

What are characteristics of Kelvin-Helmholtz waves and their associated hazards?

Characteristics - Occurs in shallow layer - Form in crest of mountain wave Hazard - Strong turbulence with strong shear

Identify conditions that are conductive for nocturnal radiation inversions

During Day - Sun warms ground - Ground warms air - Temperature decreases with height During Night - Infrared Radiation Loss - Surface Cooling - Air aloft changes little --Temperature inversion

What frontal speed produces moderate to severe turbulence

Greater than 30kts

What are the conditions that produce moderate turbulence in the boundary layer

If surface winds > 30 kts

Define boundary layer

Layer in which friction affects wind

What is the shear value for severe turbulence

More than 6 knots per 1,000 ft

Define Jet Stream

Relatively strong winds concentrated within a narrow stream in the atmosphere

Define an Eddie

Shear induced rotation of air

What are Kelvin-Helmholtz Waves?

Shear induced wave that develops in a concentrated layer

What are areas of strong shear on constant pressure charts

Shear on Polar side of Jet

What is the relationship between wind shear and stability in producing turbulence

Stability suppresses Turbulence until shear becomes so great that it overcomes stability

Characterize the stability found within frontal zones

Strong Stability 50-150 miles

Define critical shear value

The amount of shear required to produce turbulence

Define Shear Gradient. What is it measured in?

The magnitude of shear - Knots per distance

Define Wind Shear Turbulence

Turbulence that results from wind shear


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