Mountain Waves

Question 1

Where, in relation to a mountain, do mountain waves occur?

Answer 1

Over top the mountain and in the lee side.

Question 2

How fast can the vertical currents within the oscillations reach?

a) 1000 ft/min
b) 2000 ft/min
c) 2500 ft/min
d) 3500 ft/ min

Answer 2

b) 2000 ft/min

Question 3

A mountain range (or line of hills) are needed for mountain waves, what else is required?

(Think wind and stability)

Answer 3

Wind direction within 30 Deg of perpendicular to ridge
Wind speed at crest in excess of 15 kts, increasing with height
Stable air at crest ridge and less below, with less stable air above.

Question 4

The combination of strong vertical currents and surface friction may cause what to form beneath the mountain waves?

Answer 4

Rotors.

Question 5

A _____ stream nearly perpendicular to the mountain range provides ideal conditions for mountain waves.

Answer 5

Jet Stream

Question 6

True of False?

Clouds always form with mountain waves.

Answer 6

False, they only form if there is sufficient moisture.

Question 7

Which type of clouds may form due to mountain waves?

Answer 7

Cap, lenticular and rotor clouds.

Question 8

Which type of cloud results in severe to extreme turbulence?

Answer 8

Rotor clouds

Question 9

Which cloud conceals the top of a mountain?

Answer 9

Cap

Question 10

Which cloud is stationary, smooth, lens shaped and forms in wave crests parallel to the mountain range?

Bonus point: What lenticular cloud forms at the middle levels?

Answer 10

Lenticular.

BP: Altocumulus Standing Lenticularis or ACSL

Question 11

What interacts with the flow reversal to produce a rotor cloud?

Answer 11

Updrafts

Question 12

Do the strongest rotors occur with the wave nearest or furthest from the ridge?

Answer 12

Nearest

Question 13

If a rotor forms from an inversion, in which direction does the warm air/ cold air travel? Also, what warming/ cooling mechanisms are in place?

Answer 13

Warm are is rotated downward and heated further from compression. Cold air is carried aloft and cooled further by expansion.

Question 14

What is the wavelength and amplitude of a mountain wave?

Answer 14

Wavelength: 10km
Amplitude: 3 - 5000 ft.

Question 15

Do the updrafts or downdrafts produce the flow reversal in a rotor cloud?

Answer 15

Updrafts

Question 16

Rotor clouds are a sign of flow reversal and what?

Answer 16

Severe turbulence.

Question 17

At what point/ area is the wind the strongest in a lee wave flow?

Answer 17

The wave crest.

Question 18

Regarding the overall mountain wave pattern, smooth clouds and ragged/ torn clouds indicate what?

Answer 18

Smooth clouds indicate the flow is laminar and there is little turbulence

Ragged/ torn clouds means the air is turbulent.

Question 19

Is the temperature cooler is the crests or troughs at a particular level? Why?

Answer 19

Cooler in the crests (expansion cooling) and warmed in the troughs (compression warming).

Question 20

True or False?

The combined effects of airspeed fluctuations, turbulence and icing increase the chances of either stalling or over-speeding the aircraft.

Answer 20

True.

Question 21

Where are the vertical currents worse in relation to the mountain?

Answer 21

Downslope winds of the lee side of the mountain.

Question 22

Where is the most turbulent area around a mountain?

Answer 22

The rotor area.

Question 23

How does travelling downstream or upstream differ regarding turbulence?

Answer 23

Down stream: Results in more turbulence as the aircraft passes through up/ down drafts faster.

Upstream: Less turbulence but for a longer period.

Question 24

How does the lowering of pressure in wave crests effect an aircraft’s altimeter?

Answer 24

It causes an error, indicating the AC is higher than it is.

Question 25

What are some flight precautions for mountain waves?

(Think avoid, height of mountain and approach).

Answer 25

Avoid mountain wave area
Avoid rotor at all cost
Avoid strong winds on lee side of mountain
Over fly mountain by 50% of mountain height
Approach mountain range at 45 Deg angle
Approach at turbulence penetration speed.

Question 26

What are some pre-flight tips to recognize mountain waves?

Answer 26

Check upper air analyses and forecast charts for flow across the mountain range
Check satellite pictures for wave clouds
Check hourly reports for ACSL
Check pilot reports for turbulence

Question 27

What are some in-flight tips to recognize mountain waves?

Answer 27

Look for lenticular or rotor clouds

Look for raised dust, it indicated a reversed flow at surface.