Meteorology 2 Flashcards
Station Pressure
Weight of column of air lying above an airport
Altimeter Setting
- Station pressure + weight of column of air between ground and sea level
- Weight of imaginary column of air calculated using ICAO standard atmosphere
Mean Sea Level Pressure
- Station pressure + weight of column of air between ground and sea level
- Weight of imaginary column of air calculated using average temperature over previous 12 hours
Low Pressure Systems
- Cyclones
- Surround by high pressure
- Air rotates counter clockwise in northern hemisphere due to Coriolis effect
- Air converges into a low
High Pressure Systems
- Anti-cyclones
- Surround by low pressure
- Air rotates clockwise in northern hemisphere due to Coriolis effect
- Air diverges from a high
Coriolis Effect
- Atmosphere does not rotate at the same speed as the surface
- Apparent when air attempts to flow in a north south direction.
Friction Effect
- Topographical features reduce wind speed at low level
- Only occurs up to 2000-3000 AGL
Sea Breeze
- Sea to land
- During the day, the temperature of the land rises more quickly than the water
Land Breeze
- Land to sea
- During the night, the land cools more quickly than the water
Anabatic Wind
- Valley Breeze
- Occurs during the day when the sun warms the mountain sides
- Air in contact warms by conduction
- This air is less dense and rises up the mountain
Katabatic Wind
- Usually occurs during night
- Mountain sides cool quickly
- Air in contact becomes cold through conduction
- Cold air sinks to the valley below
- Can occur during the day due to snow covered slopes reflecting sunlight
Causes of Wind Shear
- Nocturnal Inversions can produce shear zones usually at 1000 AGL
- Thunderstorms
Low Level Jet Stream
- Sheet of strong winds
- Dissipates as daytime heating eliminates inversion
Air Masses
- large section of troposphere with uniform properties of temperature and moisture
- takes properties from surface over what it is formed
Cold Front Weather
Determined by the moisture content and stability of the warm air mass
Signs of Cold Front Passage
- Decrease in temp
- Wind veer and increase speed
- Falling then rising
Warm Front Weather
Determined by the moisture content and stability of the warm air mass
Signs of Warm Front Passage
- Temperature will increase
- Wind will veer gradually
- Visibility generally poorer
Frontal Depressions
- Two air masses flowing parallel to a front
- Quasi-stationary
- Cold air neither advancing nor retreating
- Wave is created due to atmospheric disturbance
- Cyclonic flow is created and low pressure system develops, along with cold and warm fronts
- Cold air moves faster and undercuts the warm air, forming an occluded front
- System weakens and then becomes a stationary front again
Occlusions
Cold front catches warm front, forcing the warm air up, called a TROWAL
Upper Fronts
- Narrow transition zone between two air masses where the temp difference does not exist at the the surface
- Sometimes a front doesn’t come right down to the surface
Causes of Upper Fronts
- Very cold air is trapped below two warmer air masses, could have a warm or cold front above it
- A very shallow warm or cold front
- Daytime heating equalizes the temperature of two air masses at a front
Aircraft Icing
Occurs when supercooled water droplets freeze on contact with a cold aircraft
Requirements for Icing
- Visible moisture
- Below freezing temperatures
- must fly through cloud below the freezing level or through freezing precipitation
Clear Ice
- Slow freezing
- High temperature
- Harder to remove
- Smooth, not as diminishing
Rime Ice
- Rapid freezing
- Low Temperature
- Easier to remove
- Brittle, very diminishing
Collection Efficiency
- Thin airfoil (horizontal stabilizer)
- High aircraft speed
- Large droplets
Trace Icing
Not hazardous unless encountered for over 1 hour
Light Icing
May be a problem if conditions persist (under 1 hour)
Moderate Icing
Short encounters become potentially hazardous, anti-icing or diversion required
Severe
Anti-icing doesn’t work, diversion necessary
Ice of a Medium Grit Sandpaper
- Lift decreases 30%
- Drag increases 40%
Tail-Plane Stall
- Tail stalls first due to high catch rate
- Don’t use flaps, increase speed
Icing in Cloud - Layer Cloud
- Freezing level to -5ºC
- Tend to have rime ice
Icing in Cloud - Vertical Cloud
- Freezing level to -15ºC
- Tend to have clear ice
Icing in Cloud - TCU or CB
Freezing level may be up to -25ºC
Frost
- Sublimation of water vapour directly onto the aircraft
- Requires a cold, clear night, or a rapid descent in below freezing temperatures (hoar frost)
Frozen Dew
- Water vapour condenses on the aircraft
- Water freezes as the temperature drops
Cold soaking
- Warm wings are filled with cold fuel
- Air adjacent to underside of wing cools, condensation or sublimation occurs
- May takeoff if POH procedures are followed
Turbulence Causes
- Windshear
- Frontal Air
- Hot air
- Surface Texture
Turbulence Classification
- Occasional (<1/3)
- Intermittent (1/3 to 2/3)
- Continuous (>2/3)
