Meteorology
The Atmosphere 01
Earth’s atmosphere main components:
● Nitrogen - 78.08%, Oxygen 20.95%, Argon 0.93%, Carbon Dioxide 0.03%, and small
amounts of others
● Amounts stay constant up to 80km height
● Components locally variable
○ Carbon dioxide - major presence close to industrialized areas
○ Ozone - significant difference between 25 and 50km height
○ Water vapour - important presence in tropical and equatorial coastal areas.
Troposphere
● Heated from the surface below (by convective currents and latent heat release)
● Turbulent layer, contains most part of the weather phenomena affecting aviation
● Average rate of temperature decrease with height 1.98 ~ 2°C/1000ft (6.5°C/km)
● Variable thickness, dependent from latitude, season and pressure at MSL
Stratosphere
● Includes almost all of the atmospheric Ozone.
● Heated by Sun’s Ultra Violet radiation absorption (UVB)
● Absence of vertical movements, stable, suitable for air navigation
● Isothermal layer up to 20km
● Temperature lapse rate increasing 1°C/km up to 32km, and 3°C/km afterwards
● Positive temperature values at the upper limit
● May show very high “nacreous clouds”
Mesosphere
● Temperature decreases up to -95°C at 80km
● Mesopause defines the homogeneous atmosphere upper limit
● May show extremely high clouds “noctilucent clouds”
Thermosphere
● Heated by Sun’s ultra violet radiation (UVC)
● Oxygen gets ionized becoming the ionosphere
● Temperature increase up to 1000 - 2000°C
● Thermosphere upper limit can be found around 500km or higher.
Tropopause
● Troposphere upper boundary, separating this one from the stratosphere
● Temperature decreases constantly with height
● Most part of the weather affecting aviation takes place below tropopause
● Height/level varies with temperature of the air below and with atmospheric pressure at sea
level.
● Lower over the poles, thus, becomes warmer - 6 to 9 km = -40 to -50 °C
● Average Tropopause height and temp. 10 - 13km = -50 to -60 °C
● Higher over the equator, thus becomes colder - 17 to 18km = -70 to -80 °C
1
,Air Density
● Density is directly proportional to pressure
● Density is inversely proportional to altitude
● Density is inversely proportional to temperature
● Density is inversely proportional to humidity
● As altitude increases, both temperature and pressure decrease
● Density decreases as altitude increases
● Density will change by 1% for a 3 degree change in temperature or a 10hPsa change in
pressure
Pressure
● Decreases with height because there is less air above, as altitude increases.
● 27feet per hPa at MSL (ISA conditions)
● 50feet at 20000ft
● 100 feet at 40000ft
● Measured in hPa = millibar
● Average pressure of the atmosphere is 1013.25 millibar or 29.92 inches of mercury
Measured by a barometer, and the most common type is the mercury barometer
Temperature
● Measure of how hot or cold the air is
● Describes the kinetic energy, or energy of motion, or gases that make up air
● Affects:
○ Rate of evaporation
○ Relative humidity
○ Wind speed and direction
○ Precipitation patterns and tyres, such as whether it will rain, snow, or sleet
● Temperature is given in °C
● T(°F) = T(°C) x 1.8 + 32
● nT(°C) = (T°F -32) / 1.8
● T(K) = T(°C) + 273
QFE - Barometric pressure at the airfield
QFF - Estimated barometric pressure at MSL. Calculated using the actual temperature of the
aerodrome
● May differ from QNH
● Pressure used to build meteorological charts
QNH - Barometric pressure at the airfield (QFE), converted to MSL using ISA temp at the airfield and
the ISA pressure lapse rate.
● Does not account for temp deviations from ISA.
➔ Atmospheric pressure values will always be rounded to the lower whole number. 1001.9hPa
> 1001 hPa
QNE - Pressure altitude of the touchdown point.
For stations above sea level:
● Warmer than ISA, QNH > QFF
● Colder than ISA, QNH < QFF
2
,For stations below sea level:
● Warmer than ISA, QNH < QFF
● Colder than ISA, QNH > QFF
Isobars - QFF pressure values are used to build MSL pressure charts. The thin continuous numbered
lines connect points with the same QFF.
Density Altitude - Altitude relative to standard atmospheric conditions ISA at which the air density
would be equal to the indicated air density
● Density altitude = pressure altitude + 120ft x (OAT - ISA Temp)
3Hs Rule - Density altitude increases with height, humid, and hot.
Pressure Altitude - Altitude in ISA with the same atmospheric pressure as that of the part of the
atmosphere.
● Pressure altitude = (1013 - current pressure setting) x 27ft + field elevation
Change of density aloft - At the surface as latitude increases temperature decreases so density will
increase as we move from the Equator towards the poles.
Altimeter
● If pressure decreases, altimeter indicated altitude will increase (higher)
● If pressure increases, altimeter indicated altitude will decrease (lower)
● If reference pressure decreases, altimeter indicated altitude will decrease(closer to terrain)
ISA
● MSL temperature of +15°C
● MSL pressure of 1013.25 hPa
● MSL density of 1225 grams / cubic metre
● Lapse rate of 1.98 °C/1000ft up to 36090feet (11km)
● Constant temperature of 56.5°C from 11km to 65617ft (20km)
● Increase in temperature of 0.3°C/1000ft from 20km to 104987ft
ISA = 15 - (height in thousands of feet x 2)
Flying altitude (from high to low look out below)
● Higher pressure - true altitude > indicated altitude
● Lower pressure - true altitude < indicated altitude
● Colder than ISA - true altitude < indicated altitude
● Warmer than ISA - true altitude > indicated altitude
Altitude - Vertical distance above MSL
Height - Vertical distance of a level or point measured from a specific datum
Elevation - Vertical distance of a fixed point above MSL
Flight Level - Surface of constant atmospheric pressure measure from the 1013 hPa datum used for
vertical separation by specified pressure intervals (500 - 1000 ft).
Transition Altitude - Altitude at or below which the vertical position of an aircraft is controlled by
reference to altitude QNH
3
, Transition Level - Lowest flight level (1013) available for use above the transition altitude
Transition Layer - Airspace between the transition altitude and transition level.
Barometric Error - Errors caused by setting a pressure on the subscale other than the correct one.
Temperature error - Altimeter is calibrated in accordance with the ISA. If temperature is other than
ISA, altimeter will be in error.
● Temperature error height correction is 4 feet per degree celsius deviation from ISA per 1000
feet.
Wind - Wind direction is always given as the direction from which the wind is blowing. Given in
degrees true (given by ATC will be in magnetic)
Gust - Sudden increase in wind speed. (only reported if 10kt or more above the mean wind speed)
Lull - Sudden decrease in wind speed.
Squalls - Sudden increase in wind speed, often with a change in direction (associated with
cumulonimbus cloud and cold fronts)
Gale - When sustained wind speed exceeds 33kt, or gusts exceeds 42kt
Hurricane - Wind exists sustained with speeds exceeding 63kts.
4
The Atmosphere 01
Earth’s atmosphere main components:
● Nitrogen - 78.08%, Oxygen 20.95%, Argon 0.93%, Carbon Dioxide 0.03%, and small
amounts of others
● Amounts stay constant up to 80km height
● Components locally variable
○ Carbon dioxide - major presence close to industrialized areas
○ Ozone - significant difference between 25 and 50km height
○ Water vapour - important presence in tropical and equatorial coastal areas.
Troposphere
● Heated from the surface below (by convective currents and latent heat release)
● Turbulent layer, contains most part of the weather phenomena affecting aviation
● Average rate of temperature decrease with height 1.98 ~ 2°C/1000ft (6.5°C/km)
● Variable thickness, dependent from latitude, season and pressure at MSL
Stratosphere
● Includes almost all of the atmospheric Ozone.
● Heated by Sun’s Ultra Violet radiation absorption (UVB)
● Absence of vertical movements, stable, suitable for air navigation
● Isothermal layer up to 20km
● Temperature lapse rate increasing 1°C/km up to 32km, and 3°C/km afterwards
● Positive temperature values at the upper limit
● May show very high “nacreous clouds”
Mesosphere
● Temperature decreases up to -95°C at 80km
● Mesopause defines the homogeneous atmosphere upper limit
● May show extremely high clouds “noctilucent clouds”
Thermosphere
● Heated by Sun’s ultra violet radiation (UVC)
● Oxygen gets ionized becoming the ionosphere
● Temperature increase up to 1000 - 2000°C
● Thermosphere upper limit can be found around 500km or higher.
Tropopause
● Troposphere upper boundary, separating this one from the stratosphere
● Temperature decreases constantly with height
● Most part of the weather affecting aviation takes place below tropopause
● Height/level varies with temperature of the air below and with atmospheric pressure at sea
level.
● Lower over the poles, thus, becomes warmer - 6 to 9 km = -40 to -50 °C
● Average Tropopause height and temp. 10 - 13km = -50 to -60 °C
● Higher over the equator, thus becomes colder - 17 to 18km = -70 to -80 °C
1
,Air Density
● Density is directly proportional to pressure
● Density is inversely proportional to altitude
● Density is inversely proportional to temperature
● Density is inversely proportional to humidity
● As altitude increases, both temperature and pressure decrease
● Density decreases as altitude increases
● Density will change by 1% for a 3 degree change in temperature or a 10hPsa change in
pressure
Pressure
● Decreases with height because there is less air above, as altitude increases.
● 27feet per hPa at MSL (ISA conditions)
● 50feet at 20000ft
● 100 feet at 40000ft
● Measured in hPa = millibar
● Average pressure of the atmosphere is 1013.25 millibar or 29.92 inches of mercury
Measured by a barometer, and the most common type is the mercury barometer
Temperature
● Measure of how hot or cold the air is
● Describes the kinetic energy, or energy of motion, or gases that make up air
● Affects:
○ Rate of evaporation
○ Relative humidity
○ Wind speed and direction
○ Precipitation patterns and tyres, such as whether it will rain, snow, or sleet
● Temperature is given in °C
● T(°F) = T(°C) x 1.8 + 32
● nT(°C) = (T°F -32) / 1.8
● T(K) = T(°C) + 273
QFE - Barometric pressure at the airfield
QFF - Estimated barometric pressure at MSL. Calculated using the actual temperature of the
aerodrome
● May differ from QNH
● Pressure used to build meteorological charts
QNH - Barometric pressure at the airfield (QFE), converted to MSL using ISA temp at the airfield and
the ISA pressure lapse rate.
● Does not account for temp deviations from ISA.
➔ Atmospheric pressure values will always be rounded to the lower whole number. 1001.9hPa
> 1001 hPa
QNE - Pressure altitude of the touchdown point.
For stations above sea level:
● Warmer than ISA, QNH > QFF
● Colder than ISA, QNH < QFF
2
,For stations below sea level:
● Warmer than ISA, QNH < QFF
● Colder than ISA, QNH > QFF
Isobars - QFF pressure values are used to build MSL pressure charts. The thin continuous numbered
lines connect points with the same QFF.
Density Altitude - Altitude relative to standard atmospheric conditions ISA at which the air density
would be equal to the indicated air density
● Density altitude = pressure altitude + 120ft x (OAT - ISA Temp)
3Hs Rule - Density altitude increases with height, humid, and hot.
Pressure Altitude - Altitude in ISA with the same atmospheric pressure as that of the part of the
atmosphere.
● Pressure altitude = (1013 - current pressure setting) x 27ft + field elevation
Change of density aloft - At the surface as latitude increases temperature decreases so density will
increase as we move from the Equator towards the poles.
Altimeter
● If pressure decreases, altimeter indicated altitude will increase (higher)
● If pressure increases, altimeter indicated altitude will decrease (lower)
● If reference pressure decreases, altimeter indicated altitude will decrease(closer to terrain)
ISA
● MSL temperature of +15°C
● MSL pressure of 1013.25 hPa
● MSL density of 1225 grams / cubic metre
● Lapse rate of 1.98 °C/1000ft up to 36090feet (11km)
● Constant temperature of 56.5°C from 11km to 65617ft (20km)
● Increase in temperature of 0.3°C/1000ft from 20km to 104987ft
ISA = 15 - (height in thousands of feet x 2)
Flying altitude (from high to low look out below)
● Higher pressure - true altitude > indicated altitude
● Lower pressure - true altitude < indicated altitude
● Colder than ISA - true altitude < indicated altitude
● Warmer than ISA - true altitude > indicated altitude
Altitude - Vertical distance above MSL
Height - Vertical distance of a level or point measured from a specific datum
Elevation - Vertical distance of a fixed point above MSL
Flight Level - Surface of constant atmospheric pressure measure from the 1013 hPa datum used for
vertical separation by specified pressure intervals (500 - 1000 ft).
Transition Altitude - Altitude at or below which the vertical position of an aircraft is controlled by
reference to altitude QNH
3
, Transition Level - Lowest flight level (1013) available for use above the transition altitude
Transition Layer - Airspace between the transition altitude and transition level.
Barometric Error - Errors caused by setting a pressure on the subscale other than the correct one.
Temperature error - Altimeter is calibrated in accordance with the ISA. If temperature is other than
ISA, altimeter will be in error.
● Temperature error height correction is 4 feet per degree celsius deviation from ISA per 1000
feet.
Wind - Wind direction is always given as the direction from which the wind is blowing. Given in
degrees true (given by ATC will be in magnetic)
Gust - Sudden increase in wind speed. (only reported if 10kt or more above the mean wind speed)
Lull - Sudden decrease in wind speed.
Squalls - Sudden increase in wind speed, often with a change in direction (associated with
cumulonimbus cloud and cold fronts)
Gale - When sustained wind speed exceeds 33kt, or gusts exceeds 42kt
Hurricane - Wind exists sustained with speeds exceeding 63kts.
4
