High Level Turbulence

Question 1

What is the main cause of turbulence above the boundary layer?

Answer 1

Strong wind shear

Question 2

Beyond strong wind shear, what are three additional causes of high level turbulence?

Answer 2

Convection, Virga and Mountain Waves

Question 3

Define Clean Air Turbulence (CAT).

Answer 3

All the turbulence in the free atmosphere of interest to aircraft ops that is not in/ adjacent to convective activity.

Question 4

There are several causes for CAT, which is the main one?

Answer 4

Strong wind Shear

Question 5

Where can CAT occur?

Answer 5

Usually in clear air, but can occur in clouds.

Question 6

In what season is CAT more likely?

Answer 6

Winter

Question 7

How does terrain influence CAT?

Answer 7

CAT occurs and is more severe over mountains than over the Prairies or oceans.

Question 8

On a flight through a CAT area, there is a ___% chance of turbulence.

a) 25%
b) 40
c) 50%
d) 75%

Answer 8

c) 50%

Question 9

Vertical wind shears above and below a jet stream are ____ kts / ____ ft.

Answer 9

3-10 kts per 1000 ft.

Question 10

What is the vertical threshold speed for CAT?

Answer 10

5 kts / 1000 ft.

Question 11

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

Answer 11

24-100

Question 12

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

Answer 12

8-30 kts / 100 nm

Question 13

What is the horizontal threshold speed for wind CAT?

Answer 13

30 kts / 100 nm

Question 14

Of the varying levels of turbulence (Light to Extreme), which ones cause changes in aircraft altitude, either small or large?

Answer 14

Moderate, Moderate Chop, Severe, and Extreme.

Question 15

Which levels of turbulence may cause the aircraft to out of control?

Answer 15

Severe to Extreme

Question 16

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

Answer 16

a) Light
b) Severe
c) Moderate

Question 17

Where are winds the strongest in relation to the tropopause?

Answer 17

Just below it

Question 18

Turbulence normally stops within ____ ft above the tropopause.

a) 1000
b) 1500
c) 2000
d) 3000

Answer 18

c) 2000

Question 19

Define Virga

Answer 19

Precipitation that evaporates before reaching the ground.

Question 20

Explain the virga process, does it cause up or down drafts?

Answer 20

Precipitation evaporates using the heat from the surrounding air. The air is now colder than its environment so down drafts occur.

Question 21

What does virga cause?

Answer 21

Strong down drafts, wind shear and turbulence; possible microburst.

Question 22

Does virga cause air to move up or downward at a significant rate?

Answer 22

Downward

Question 23

Explain the dimensions of CAT.

Answer 23

Generally shallow, narrow and elongated.

Question 24

True of False?

The patchy nature of CAT makes PIREPs useful to briefers, ATC, forecasters etc…

Answer 24

True, precise forecasts are not possible with CAT.