Mountain Waves Flashcards
Where, in relation to a mountain, do mountain waves occur?
Over top the mountain and in the lee side.
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
b) 2000 ft/min
A mountain range (or line of hills) are needed for mountain waves, what else is required?
(Think wind and stability)
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.
The combination of strong vertical currents and surface friction may cause what to form beneath the mountain waves?
Rotors.
A _____ stream nearly perpendicular to the mountain range provides ideal conditions for mountain waves.
Jet Stream
True of False?
Clouds always form with mountain waves.
False, they only form if there is sufficient moisture.
Which type of clouds may form due to mountain waves?
Cap, lenticular and rotor clouds.
Which type of cloud results in severe to extreme turbulence?
Rotor clouds
Which cloud conceals the top of a mountain?
Cap
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?
Lenticular.
BP: Altocumulus Standing Lenticularis or ACSL
What interacts with the flow reversal to produce a rotor cloud?
Updrafts
Do the strongest rotors occur with the wave nearest or furthest from the ridge?
Nearest
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?
Warm are is rotated downward and heated further from compression. Cold air is carried aloft and cooled further by expansion.
What is the wavelength and amplitude of a mountain wave?
Wavelength: 10km
Amplitude: 3 - 5000 ft.
Do the updrafts or downdrafts produce the flow reversal in a rotor cloud?
Updrafts
Rotor clouds are a sign of flow reversal and what?
Severe turbulence.
At what point/ area is the wind the strongest in a lee wave flow?
The wave crest.
Regarding the overall mountain wave pattern, smooth clouds and ragged/ torn clouds indicate what?
Smooth clouds indicate the flow is laminar and there is little turbulence
Ragged/ torn clouds means the air is turbulent.
Is the temperature cooler is the crests or troughs at a particular level? Why?
Cooler in the crests (expansion cooling) and warmed in the troughs (compression warming).
True or False?
The combined effects of airspeed fluctuations, turbulence and icing increase the chances of either stalling or over-speeding the aircraft.
True.
Where are the vertical currents worse in relation to the mountain?
Downslope winds of the lee side of the mountain.
Where is the most turbulent area around a mountain?
The rotor area.
How does travelling downstream or upstream differ regarding turbulence?
Down stream: Results in more turbulence as the aircraft passes through up/ down drafts faster.
Upstream: Less turbulence but for a longer period.
How does the lowering of pressure in wave crests effect an aircraft’s altimeter?
It causes an error, indicating the AC is higher than it is.
What are some flight precautions for mountain waves?
(Think avoid, height of mountain and approach).
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.
What are some pre-flight tips to recognize mountain waves?
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
What are some in-flight tips to recognize mountain waves?
Look for lenticular or rotor clouds
Look for raised dust, it indicated a reversed flow at surface.
