High Level Turbulence Flashcards
What is the main cause of turbulence above the boundary layer?
Strong wind shear
Beyond strong wind shear, what are three additional causes of high level turbulence?
Convection, Virga and Mountain Waves
Define Clean Air Turbulence (CAT).
All the turbulence in the free atmosphere of interest to aircraft ops that is not in/ adjacent to convective activity.
There are several causes for CAT, which is the main one?
Strong wind Shear
Where can CAT occur?
Usually in clear air, but can occur in clouds.
In what season is CAT more likely?
Winter
How does terrain influence CAT?
CAT occurs and is more severe over mountains than over the Prairies or oceans.
On a flight through a CAT area, there is a ___% chance of turbulence.
a) 25%
b) 40
c) 50%
d) 75%
c) 50%
Vertical wind shears above and below a jet stream are ____ kts / ____ ft.
3-10 kts per 1000 ft.
What is the vertical threshold speed for CAT?
5 kts / 1000 ft.
HWS speeds on the cold side of the jet are ____ kts / 100 nm.
a) 15-20
b) 24-100
c) 45-90
d) 50 -100
24-100
HWS on the warm side of a jet stream is ____ kts / 100 nm.
a) 2-6
b) 5-10
c) 8-30
d) 10-45
8-30 kts / 100 nm
What is the horizontal threshold speed for wind CAT?
30 kts / 100 nm
Of the varying levels of turbulence (Light to Extreme), which ones cause changes in aircraft altitude, either small or large?
Moderate, Moderate Chop, Severe, and Extreme.
Which levels of turbulence may cause the aircraft to out of control?
Severe to Extreme
Which levels of turbulence have the following air speed fluctuations:
a) Less than 15 kts
b) Excess of 25 kts
c) Between 15-25 kts
a) Light
b) Severe
c) Moderate
Where are winds the strongest in relation to the tropopause?
Just below it
Turbulence normally stops within ____ ft above the tropopause.
a) 1000
b) 1500
c) 2000
d) 3000
c) 2000
Define Virga
Precipitation that evaporates before reaching the ground.
Explain the virga process, does it cause up or down drafts?
Precipitation evaporates using the heat from the surrounding air. The air is now colder than its environment so down drafts occur.
What does virga cause?
Strong down drafts, wind shear and turbulence; possible microburst.
Does virga cause air to move up or downward at a significant rate?
Downward
Explain the dimensions of CAT.
Generally shallow, narrow and elongated.
True of False?
The patchy nature of CAT makes PIREPs useful to briefers, ATC, forecasters etc…
True, precise forecasts are not possible with CAT.
