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17 Cards in this Set
- Front
- Back
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Define mountain waves
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- waves or ripples in the atmosphere caused by air encountering an obstruction or barrier at the surface of the earth
403.1.1 |
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Mountain waves formation
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- air dips down lee side of ridge
- >1000 meter drop especially conducive to formation - wave crests extend downwind for many km 403.1.2 |
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List the 4 factors that affect the evolution of mountain waves
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- obstruction
- stable layer - strong wind - weak directional shear 403.1.3 |
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Describe obstruction as a factor that affects the evolution of mountain waves
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- disturbs horizontal air flow
- wave pattern produced across troposphere - wavelength and strength of vertical currents affected by width of obstruction - amplitude and strength of vertical currents affected by lee side fall - waves immediately following obstruction are strongest, progressively weaker downstream 403.1.4 |
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Describe stable layer as a factor that affects the evolution of mountain waves
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- must be present just above the crest
- stable air resists rising motion of wave - sinking air warms and rises back up as a wave 403.1.4 |
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Describe strong wind as a factor that affects the evolution of mountain waves
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- 25 kt minimum speed
- angled wind has diminished strength and stronger speed required - 30 degree angle of incidence max allowable deviation - presence of jet stream assists with speed of wave 403.1.4 |
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Describe weak directional shear as a factor that affects the evolution of mountain waves
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- uniform direction maintains organized standing wave pattern
403.1.4 |
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List the 3 cloud types associated with mountain waves
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- cap
- rotor - lenticular 403.2.1 |
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Describe the development of cap cloud associated with mountain waves
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- formed by orographic lift
- adiabatic cooling forms cloud on windward side - adiabatic heating dissipates cloud on leeward side 403.2.2 |
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Describe the development of rotor cloud associated with mountain waves
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- result of turbulent mixing
- appear as long line of SC - CB can be associated - can be extremely turbulent 403.2.2 |
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Describe the development of lenticular cloud associated with mountain waves
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- formed at wave crests
- form on upwind side and dissipate on downwind side through adiabatic cooling/heating - most common clue that lee waves present - most common in mid levels as ACSL 403.2.2 |
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List the 5 hazards to aviation associated with mountain waves
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- up/downdrafts
- changes in pressure - turbulence - vertical wind shear - obscured terrain 403.3.1 |
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Describe up/downdrafts as a hazard to aviation associated with mountain waves
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- may force changes in altitude of aircraft
- downdrafts most severe near a mountain - possible for aircraft to be forced onto the ground 403.3.2 |
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Describe changes in pressure as a hazard to aviation associated with mountain waves
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- increased wind speed in crests cause local lowering of pressure
- causes error in altimeter reading 403.3.2 |
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Describe turbulence as a hazard to aviation associated with mountain waves
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- rotor cloud most turbulent area in mountain wave system
- can be as severe as any turb encountered in atmosphere - strongest rotor occurs with wave nearest the ridge 403.3.2 |
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Describe vertical wind shear as a hazard to aviation associated with mountain waves
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- jet stream turbulence greatly increased over high ground
- mountain waves more pronounced on warm side of jet stream 403.3.2 |
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Describe obscured terrain as a hazard to aviation associated with mountain waves
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- higher terrain masked by cap cloud
403.3.2 |
