ATPL METEOROLOGY NOTES
written by
the airline pilot
1
2021
, METEOROLOGY NOTES
Meteorology Data Sheet for ATPL
Chapter 1 – The Atmosphere
ISA
Mean Sea Level (MSL) Temperature 15°C
Pressure 1013.25 hPa
Density 1225 gm-3
From MSL to 11 km (36 090 ft) Temperature decreases at 6.5°C per km
(1.98°C per 1000 ft)
From 11 km to 20 km (65 617 ft) Temperature constant at –56.5°C
From 20 km to 32 km (104 987 ft) Temperature rises with height at 1°C per km
(0.3°C per 1000 ft)
Composition
Nitrogen 78.09%
Oxygen 20.95%
CO2 0.03%
Argon 0.93%
Rest rare gases
Troposphere Depth varies with latitude and season. Temperate latitudes up to 11Km
Tropopause Boundary between the Troposphere and theStratosphere.
Temperature becomes Isothermal.
The height of the tropopause varies with latitude, season and surface
temperature
Latitude Height Temperature
Equator 55 000 ft 17 Km -75°C
50° 35 000 ft 11 Km -55°C
Pole 25 000 ft 7 Km -45°C
In Equatorial regions flights take place below the tropopause; in temperate regions flights are
above the tropopause.
l
,Stratosphere 11 – 50 Km. Initially Isothermal becoming aninversion
CB can penetrate well into the Stratosphere
Stratopause Boundary between the Stratosphere and theMesosphere
Mesosphere 50 – 80 Km
Mesopause Boundary between the Mesosphere and theThermosphere
Thermosphere 80 Kmupwards
l
,Troposphere In immediate contact with theearth.
Contains 80% of the atmosphere, with ½ the mass in the first 18 000 ft
Contains more than 90% of all water vapour – most of the weather found in the Troposphere.
Water vapour is the most important constituent in the atmosphere from a weather stand-point.
Inversion Temperature increase with height
Isothermal Temperature remains constant withheight
Advection The horizontal motion ofair
Subsidence The vertically downwards motion ofair.
Air warms adiabatically in the descent
Convection The upward motion of air
Air cools adiabatically in the ascent.
Convergence The inward horizontal motion ofair
Convergence at height means high pressure at the surface
and little or no cloud.
Divergence The outward horizontal motion of air
Divergence at height means falling pressure at the surface
and the likely formation of convective cloud
Heating oftheAtmosphere The radiation of the sun heats the surface of the earth, which
heats the air in the troposphere frombelow.
Insolation INcoming SOLar radiATION. The solar radiation striking Earth or
anotherplanet.
Heat distributed by:
Convection - Greatest overland in the mid-afternoon insummer.
Conduction
Radiation
Latent Heat ofCondensation
Advection
Turbulentmixing
Absorption of long waveradiation
TwomostimportantfactorsareconvectionandtheLatentHeatofCondensation
DiurnalVariation The daily fluctuation of temperature. The diurnal variationin
temperature:
Is highest when the sky is clear and the wind isweak
Is lowest when there is cloud cover and a strongwind
MaximumTemperature 2 hours after 1200LMT
Clear sky, light wind
MinimumTemperature ½ hour afterdawn
Clear sky, light wind
2
, Meteorology Data Sheet
Conversion of Metres per second to Knots
Double the speed in metres per second to get the speed in knots
20 mps ~ 40 knots
TemperatureCalculations
Use the ISALapse Rate 2°C/1000 ft or 0.65°C/100 metres
Kelvin °K = °C +273
Example1 The 0ºC isotherm is forecast to be at FL 50. At what FL would you
expect a temperature of-6ºC?
Need to lose 6°C which is the equivalent to 3000 ft
Answer FL80
Example2 The temperature at 10 000 FT in the ICAO Standard Atmosphereis:
Surface TemperatureinISA +15°C
Lapse for 10000ft (2x10) -20°C
Answer ISATemperature (+15–20) -5ºC
Example3 An outside air temperature of -35ºC is measured while cruising at FL
200.
What is the temperature deviation from the ISA at thislevel:
Surface TemperatureinISA +15°C
Lapse for 20 000 ft (2 x 20) -40°C
ISA Temperature (+15 – 40) -25ºC
Actualtemperature -35°C
Temperature is 10°C lower than ISA
Answer ISADeviation -10°C
Example4 The temperature on the 300 hPa chart is -48ºC, the tropopause is at
FL 330. What is the most likely temperature at FL350?
Remember that the temperature becomes isothermal at the
Tropopause
300 hPa ~ 30 000 ft
Actual temperature at30000 -48°C
Calculate to FL 330 using ISA lapserate
3x -2 -6°C
Answer Temperature -54°C
3
written by
the airline pilot
1
2021
, METEOROLOGY NOTES
Meteorology Data Sheet for ATPL
Chapter 1 – The Atmosphere
ISA
Mean Sea Level (MSL) Temperature 15°C
Pressure 1013.25 hPa
Density 1225 gm-3
From MSL to 11 km (36 090 ft) Temperature decreases at 6.5°C per km
(1.98°C per 1000 ft)
From 11 km to 20 km (65 617 ft) Temperature constant at –56.5°C
From 20 km to 32 km (104 987 ft) Temperature rises with height at 1°C per km
(0.3°C per 1000 ft)
Composition
Nitrogen 78.09%
Oxygen 20.95%
CO2 0.03%
Argon 0.93%
Rest rare gases
Troposphere Depth varies with latitude and season. Temperate latitudes up to 11Km
Tropopause Boundary between the Troposphere and theStratosphere.
Temperature becomes Isothermal.
The height of the tropopause varies with latitude, season and surface
temperature
Latitude Height Temperature
Equator 55 000 ft 17 Km -75°C
50° 35 000 ft 11 Km -55°C
Pole 25 000 ft 7 Km -45°C
In Equatorial regions flights take place below the tropopause; in temperate regions flights are
above the tropopause.
l
,Stratosphere 11 – 50 Km. Initially Isothermal becoming aninversion
CB can penetrate well into the Stratosphere
Stratopause Boundary between the Stratosphere and theMesosphere
Mesosphere 50 – 80 Km
Mesopause Boundary between the Mesosphere and theThermosphere
Thermosphere 80 Kmupwards
l
,Troposphere In immediate contact with theearth.
Contains 80% of the atmosphere, with ½ the mass in the first 18 000 ft
Contains more than 90% of all water vapour – most of the weather found in the Troposphere.
Water vapour is the most important constituent in the atmosphere from a weather stand-point.
Inversion Temperature increase with height
Isothermal Temperature remains constant withheight
Advection The horizontal motion ofair
Subsidence The vertically downwards motion ofair.
Air warms adiabatically in the descent
Convection The upward motion of air
Air cools adiabatically in the ascent.
Convergence The inward horizontal motion ofair
Convergence at height means high pressure at the surface
and little or no cloud.
Divergence The outward horizontal motion of air
Divergence at height means falling pressure at the surface
and the likely formation of convective cloud
Heating oftheAtmosphere The radiation of the sun heats the surface of the earth, which
heats the air in the troposphere frombelow.
Insolation INcoming SOLar radiATION. The solar radiation striking Earth or
anotherplanet.
Heat distributed by:
Convection - Greatest overland in the mid-afternoon insummer.
Conduction
Radiation
Latent Heat ofCondensation
Advection
Turbulentmixing
Absorption of long waveradiation
TwomostimportantfactorsareconvectionandtheLatentHeatofCondensation
DiurnalVariation The daily fluctuation of temperature. The diurnal variationin
temperature:
Is highest when the sky is clear and the wind isweak
Is lowest when there is cloud cover and a strongwind
MaximumTemperature 2 hours after 1200LMT
Clear sky, light wind
MinimumTemperature ½ hour afterdawn
Clear sky, light wind
2
, Meteorology Data Sheet
Conversion of Metres per second to Knots
Double the speed in metres per second to get the speed in knots
20 mps ~ 40 knots
TemperatureCalculations
Use the ISALapse Rate 2°C/1000 ft or 0.65°C/100 metres
Kelvin °K = °C +273
Example1 The 0ºC isotherm is forecast to be at FL 50. At what FL would you
expect a temperature of-6ºC?
Need to lose 6°C which is the equivalent to 3000 ft
Answer FL80
Example2 The temperature at 10 000 FT in the ICAO Standard Atmosphereis:
Surface TemperatureinISA +15°C
Lapse for 10000ft (2x10) -20°C
Answer ISATemperature (+15–20) -5ºC
Example3 An outside air temperature of -35ºC is measured while cruising at FL
200.
What is the temperature deviation from the ISA at thislevel:
Surface TemperatureinISA +15°C
Lapse for 20 000 ft (2 x 20) -40°C
ISA Temperature (+15 – 40) -25ºC
Actualtemperature -35°C
Temperature is 10°C lower than ISA
Answer ISADeviation -10°C
Example4 The temperature on the 300 hPa chart is -48ºC, the tropopause is at
FL 330. What is the most likely temperature at FL350?
Remember that the temperature becomes isothermal at the
Tropopause
300 hPa ~ 30 000 ft
Actual temperature at30000 -48°C
Calculate to FL 330 using ISA lapserate
3x -2 -6°C
Answer Temperature -54°C
3
