MOUNTAIN WAVES Flashcards
Mountain waves, winds and Turbulence:
Oscillations on the Lee side (down wind) side of a mountain caused by the disturbances in the horizontal air flow due to terrain that is in the way.
How does the most common mountain wave form?
As winds are forced up an impeding mountain range, and than defends down the other side.
Where are down drafts the most severe?
Near the mountain or mountain ridges and about the same height as the summit
How fast can a down draft reach?
83 FPS, or 5000 FPM
What angle must wind direction be?
Within 30 degrees perpendicular to the mountain, and must be 25 kt or more on the windward side
What two parts are the mountain waves composed of?
Amplitude
Wavelength
What factors can change wave length?
Stability
Wind speed
Lateral positioning of ridges
Ridge spacing
Amplitude is what?
Half the vertical distance from the wave trough to the crest.
What is generally true regarding amplitudes and wavelengths?
The greater the amplitude=the shorter the wave length
What can change the Amplitude of a wave?
Stability
Mountain size
Mountain shape
Sharp Lee side
(Drops in 3000 ft cause the largest amplitudes)
Orographic clouds caused by?
Air is forced to rise by the earth’s topography
What is required for clouds to form?
Sufficient moisture
What can give us an indication that mountain waves/turbulence exist?
Lenticular clouds
Rotor clouds
Cap clouds
Banner clouds
Lenticular clouds
Typically 20-40,000ft
Form in the crests of the waves
How do METARS/ PIREPS Report Lenticular clouds?
ACSL - Alto Cumulus Standing Lenticular
CCSL- Cirro Cumulus - Standing Lenticular
Roll/Rotor Clouds:
Another indicator of mountain wave presence. They process the greatest amounts of turbulence
Where will Roll/rotor clouds form?
These will form down wind from each wave crest and within the lower turbulent zone.
Where is the Roll/rotor clouds center of rotation?
Typically near the ridgeline.
Rotor clouds intensity?
2000-5000 FPM
Produce severe turbulence
The first rotor is typically the most intense although ALL of them spell trouble
What may result with a mountain wave and a nonstandard temperature regarding the altimeter reading?
It may over read by as much as 3000 ft
Anabatic winds
Sun side of a mountain slope heats up
Warm air rises creating an upwind flow
Pockets of turbulence can occur as different parts of mountain heat up at different rates
Katabatic winds
A wind that flows down the slope of mountain. More powerful At nights when radiation cooling starts to happen at night. Blowing down glaciers = extreme katabatic
Funnel winds = decreased pressure =
Error in altimeter reading
Next to thunderstorms, what is the worst meteorological hazard we pilots face?
Mountain turbulence, in particular Rotor turbulence
If caught in down draft what should you do?
Speed up to get out of it sooner
