Local Winds Inversions Cloud Vis Fog Flashcards
Katabatic winds
Usually during nighttime
Hill face cools and gravity helps pull cool air down hill
Anabatic winds
Generally after sunrise east facing slopes
Valley face heats and warm air blows up valley face
Opposing gravity so often less extreme than katabatic
Fohn wind
Moist air blows up hill and saturated dry air blows down hill warming at dalr resulting in warmer air on leeward side
Low pressure on leeward side sucks air downhill
Fohn wind conditions
Only occurs if enough moisture for salr to create temperature difference
Lee side
Gusty and turbulent
Reduced visibility due to dust and rock particles
Large scale interference
Mountain waves standing waves lee waves
Requirements:
Large mountain range
Wind at right angles to mountain range
Unstable lower atmosphere and stable upper atmosphere
Wind speed greater than or equal to 15 kts or more
Altocumulus lenticularis
Formed by wave
Appears stationary but constantly forming and dissipating
How to avoid mountain waves
Fly on windward coast
fly high
Use local knowledge
Rotor zones and streaming
Occur in lee of range
Essentially Eddie’s
Creates circular wind flow back towards mountains
Condensed air as it accelerates can form cloud
Clouds associated with mountain wave
Rotor cloud
Wave cloud
Cap cloud
Subsidence inversion
Occurs during anti cyclones (high pressure)
Upper level convergence low level divergence
Descending air is warming at a rate that makes it warmer than ascending air
Can create anti cyclonic gloom (clouds)
Radiation inversion
Air close to ground cools during night middle layer unaffected
Requires light wind and clear sky’s
Turbulence inversion
Top of friction layer
Induced by wind of at least 10kt
Air becomes turbulent and tumbling mixing cooling and warming eventually offsetting
Frontal inversion
Warm air forced over top of colder air
Inversion occurs at boundary between the two air masses
Five lifting mechanisms
Orographic lifting
Mechanical lifting
Thermal lifting (convection)
Slow widespread ascent
Frontal lifting
Cloud formation
Lifting air gets less pressure (cooling mechanism as less collisions because parcel expands)
Convective rising
ELR must exceed DALR
Always creates cu type cloud
Can be cb or tcu
Slow widespread ascent
Low pressure
Air rises at centre and cools andiabatically
Bergeron
Water vapour depositing (gas to solid) onto ice crystals
Coalescence
Combining cloud droplets
Small ones drawn to large droplet
LCL
lifting condensation level
Dew point reduces at .6° per. 1000’
When parcel reaches dew point LCL is reached
Convective condensation level
Thermal rising
Wire must reach convective temp then follows LCL process
Used for TS calculations
Cloud dispersal
Most commonly through subsidence
Warming of air through radiation
Warming of low level air
Reduction in convective activity
Mixing
4 types of visibility
Transparency
Measure of stuff in the air expressed as distance
Illumination
Not effected by sun or moon
Range
Is effected by light
Snow detrimental
Slant range
Looking through fog at angle reduces visibility
Fog vs mist
Fog is below 1000 m vis
Mist is 1000-5000 m vis
Rain vis nz
4-10 km
Haze
Below 5000m vis
Below 1000m is a dust storm
Auto Metar vis
Handar vis sensor
Measures light scattering between two sources
Radiation fog
Anti cyclonic
Nighttime
Earth cools air above to saturation
Light wind causes mixing
High Rh
Advection fog
Warm humid air entering cool area surface
Valley fog
Cold air gathers at bottom of valley
Often rivers provide moisture
Valleys tend to get less sunlight
Stream fog
Over oceans
Occurs in cold areas near warm
Frontal fog
Warm front
Streaming fog
After a heavy shower or ts
Sun comes out and evaporates moisture
