1. Introduction Flashcards
Air pressure
Decreases w/ height
Fewer air molecules with increased altitude
Air density decreases w/ height
Cold and warm Air temperature
Cold air molecules move slower and takes up less space; air has a higher density
Warm/hot air molecules more faster and takes up more space; air will have less density
High water vapour
Low air density and pressure
Low water vapour
High air density and pressure
Does air density increase or decrease with height?
Decreases
What is the boundary layer?
Lowest part of atmosphere, surface to 3000’
What are the characteristics of the boundary layer
- Wind increases with height
- Vertical currents occur as a result of friction of wind with earth’s surface
- Tends to be turbulent because of eddies in the wind flow caused by overturning of air
- Deeper in the summer, shallower in winter
- Deeper during the day, shallower at night
- Subject to cloud formation
What is the relationship between air temp and air moisture?
The higher the temp, the more moisture it can hold
What is evaporation?
Liquid to gas
Sublimation
Solid to gas
Condensation
Gas to liquid
Melting
Solid to liquid
Deposition
Gas to solid
Freezing
Liquid to solid
Dew point temp (Td)
Temp to which air must be cooled in order for condensation to occur
Always lower or equal to air temp
Air saturation
Max amount of water vapour air can hold
Relative humidity
Amount of water vapour that is in the air relative to the amount of water vapour the air can hold at that temp
Conduction
Heat transfer through physical contact, slow process
Convection
Heat transfer by the motion of fluids, faster than conduction
Radiation
Heat transfer by electromagnetic waves, fastest
Advection
Heat transfer by horizontal flow of a fluid in the atmosphere or sphere
Radiation warming
Heat from the sun, ground warms faster than water
Advection warming
Cold air moving over a warmer surface heated by conduction
Compression warming
Air descending down the side of a hill hill encounter higher pressure and compresses and warms
Atmospheric cooling reasons
- The increase in density of the air
2. When moist air cools it creates clouds, fog and precipitation in the lower levels
Radiation cooling
Earth giving off heat without the Sun to reheat
Advection cooling
Warm air moves over cold surface
Expansion cooling
Air rises it reaches areas of lower pressure, it expands and cools
Atmospheric vertical stability
Directly related to the changes of temp with height
Characteristics of unstable air
1 cumuliform clouds
- Showery precipitation
- Turbulence
- Good Wis except in blowing obstruction
Characteristics of stable air
- stratiform clouds and fog
- Continuous precipitation
- Smooth air
- Fair to poor vis in lat and smoke
What does a stable atmosphere mean?
There is no vertical overturning
What are some of the characteristics of an unstable atmosphere to aircrew?
Turbulence, gusty winds, good vis, convective clouds, thunderstorms
What are some of the characteristics of a stable atmosphere?
Smooth flying, layered clouds, continuous precipitation
When is air most stable over the North Atlantic
Spring and summer
How does icing affect an aircraft
Decreases lift on take off, reduce power, restricts the performance
