Local Winds Flashcards
Describe the general characteristics of a mountain wave set-up with reference to wave length.
- 5 - 40km wave-lengths
- Wind 15kts at sea level acceleration as it climbs
- 90 degrees wind direction (+/- 30 degrees)
- Unstable low air, stable crest air.
Describe the general characteristics of a mountain wave set-up with reference to position and rotation of possible rotor zones.
- Anchored in position
- Side of rotor nearest the mountain rotates up
- Side furthest away rotates down
- This rotation is opposite for the upper level rotors
Describe the general characteristics of a mountain wave set-up with reference to position and type of any possible cloud development.
- Cumuliform cloud pushing up mountain
- Altocumulus lenticular cloud downstream in top of lee wave above mountain top leve
- Rotor cloud in lee of mountain below wave crest
- Cap clouds on the mountain ridge
Describe the general characteristics of a mountain wave set-up with reference to the heights of the friction layer.
- 2000 - 3000ft above surface
- Winds get faster above the layer
Describe the general characteristics of a mountain wave set-up with reference to areas of probable severe turbulence.
- Rotor zones on lee side = severe turbulence
- In high amplitude waves due to them breaking apart
- Strongest rotor is normally the first wave downwind
Describe the general characteristics of a mountain wave set-up with reference to areas of possible serve airframe icing.
- In Cb clouds building up on windward side of mountain
- In lenticular cloud
- Above the freezing level in visible level in visible moisture
With reference to mountain waves explain the factors that affect the wave amplitude.
- Shapes of the mountains ranges as the wind flows through
- Vertical extent of mountain/how steep
- Strong inversion at crest will reduce amplitude
With reference to mountain waves explain the factors that affect the wave-length.
- Lee shape steeper = longer
- Increased wind speed = longer
With reference to mountain waves, describe the flight conditions associated with mountain waves.
- Updraughts portion of wave is smooth as long as not broken.
- Downdraught portion smooth but hard to maintain height
- Rotor zones are below lenticular and either side of them
- Will be severe turbulence
Explain the rotor streaming process.
Same formation as rotor zones except:
- Wind speed decreases above mountain height instead of increasing
- Forms at or below ridge top height
- Not anchored, moves downstream
Describe the flight conditions associated with rotor streaming.
- Severe turbulence
- Worst immediately in the lee of the range
- Reduces in strength the further it gets from the range
Define the Fohn wind.
- Warm
- Dry
- Gusty
- Lee side of mountain range
State the requirements for the development of a Fohn wind.
- Substantial mountain range
- 90degree wind direction (+/- 30degree) relative to the mountains
- High moisture content
Describe the flight conditions when flying in Fohn conditions to windward of the mountain range.
- Thunderstorms
- Large amounts of rainfall/poor visibility
- Severe icing above freezing level
- Updraughts
Describe the flight conditions when flying in Fohn conditions over the mountain range.
- Weather transitions from thunderstorms/rain to SKC
- Air will stop rising level out and start descending
Describe the flight conditions when flying in Fohn conditions on the lee side of the mountains.
- Gusty wind
- Warm temperatures
- Dry air
Describe the development of sea breezes about the islands of the sub-tropical SW Pacific.
- High pressure systems over the ocean are moving to lower pressure systems over the land.
Describe the south-east trade winds about the islands of the sub-tropical SW Pacific.
- Sub tropical = 23.5 - 35 latitude
- Strong inversion the winter than summer
- Winds come from semi permanent highs at 30 degrees latitude.
Describe the development of sea breezes about the islands of the sub-tropical SW Pacific
- Strongest sea breezes occur on east side of islands
- Common throughout the year in sub tropics
- In NZ, common in late spring/early summer
Describe a katabatic wind.
- Downhill wind
- Stronger/faster than anabatic due to gravity
- 20-25kts
- Can reach speeds of 100kts
Describe an anabatic wind.
- Uphill wind
- Weaker/slower than katabatic
- 5kts
Describe the conditions that support the development of katabatic winds.
- Steep/sloping ground in mountains
- Early evening to dawn
- Slack pressure gradient
- Clear/cold conditions (winter best)
Describe the conditions that support the development of anabatic winds.
- Slope warms in afternoon, causing air close to surface to rise.
- Stronger in summer
