01 Atmosphere Flashcards
What is the composition of dry air?
Nitrogen 78%
Oxygen 21%
Other gases 1% (Argon, carbon dioxide, hydrogen, ozone, water vapour and carbon monoxide)
Layers of the Atmosphere?
Troposphere
Tropopause (boundary)
Stratosphere
Stratopause (boundary)
Mesosphere
Mesopause (boundary)
Thermosphere
What is the Troposphere?
Temperature decreases with height (rate is 2°C per 1000 ft or 0.65°C per km).
Temperature becomes almost constant (isothermal).
Contains about 75% of atmosphere’s mass.
Contains almost all of the water vapour.
Layer is about 11km thick.
What is the Tropopause?
Polar is lower and warmer.
Equatorial is higher and colder.
Height varies with latitude and is determined by surface temperature.
What is the seasonal Tropopause height?
Winter: 26,000 ft/8km over the poles.
Summer: 60,000ft 18km
What’s the standard stratosphere?
Temperature constant up to 20km (65,600 ft).
Above 20km (FL650) temperature increases due to ozone.
Advantageous due low density and lack of weather.
What is Ozone?
90% within the stratosphere.
Absorbs short-wave (UV) radiation from the sun, helping to shield the earth.
Cabin air quality at high altitude is affected more by ozone and is a respiratory irritant.
Trans polar routes more hazardous due lower tropopause.
What is the standard Mesosphere?
Temp decreases with height up to mesopause.
Noctilucent cloud can form in the mesosphere.
What is Thermosphere?
Temp increases with height, up to about 2000°C.
Contains the Ionosphere which consists of ionised molecules which affect radio communication.
ISA values at mean sea level are:
Temperature: + 15°C
Pressure: 1013.25 hPa
Density: 1.225 kg/m3
What is ISA temperature Lapse Rate?
Temperature changes at rate of 1.98°C/1000ft (0.65°C/100m).
Reduces with altitude up to 11km.
Remains constant at -56.5°C up to 20km.
From 20km, temperature increases with altitude.
ISA pressure Lapse Rate
The atmosphere’s mass is concentrated nearer the surface.
The rate of change of pressure reduces with height.
1hPa for every 30ft or (9m) of height.
Pressure decreases with altitude at a decreasing rate.
To calculate ISA temperature?
ISA = +15 - (height in 1000s of feet x 2) or
ISA = +15 - (height in km x 6.5)
To calculate ISA deviation?
ISA DEV = OAT (given in question) - ISA TEMP
e.g. -14 - -9= -5
