ATPL - Meteorology

I develop this document while studying for my EASA ATPL exams. To accomplish this I studied the Oxford Manual and did the Aviation Exam database. The information is brief and easy to read. I believe it contains all the information you will need to pass your exam. I hope you like it and can use it to study for Meteorology!

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Meteorology
Tropopause/Troposphere
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Troposphere
- Concerns aviators
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Tropopause
- Mid-latitudes ISA: 11km & -56.5°C
- Equator: 16km & -75°C
- Tropical (area around equator) tropopause 54000ft
- Separates troposphere with stratosphere
- Lower in summer, higher in winter
- Temp higher at poles
- Temp lapse rate changes abruptly
- Breaks: Core of jetstreams found here
- Area where temp change does not exceed 2/3 of 1°C/1000ft in altitude range of 6000ft
- Higher temperature of airmass = higher pressure & higher tropopause
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Stratosphere
- Ozone contained
- Layer absolutely stable
- Lower part temperature constant
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Stratopause
- 50km
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Determining Tropopause height with formula: 16km (winter) or 18km (Summer) x cos latitude
Temperature
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Insolation(Downward):
- Earth heating from heat energy from the sun, partly absorbed by atmosphere, partly reflected by clouds
mostly reaches surface
- Insolation max at noon
- Amount of heat depends on sun’s elevation & duration of insolation.
- Most significant warming is through convection(upward currents of air bringing heat) & condensation(release
of latent heat) of air
- Variation of solar energy at earth’s surface is the primary cause of weather
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Terrestrial radiation(Upward):
- Heat energy from the earth radiates to space/atmosphere/troposphere
- The clouds blocks radiation from slipping to space(from surface) i.e. clear nights = colder
- The main methods of heat transfer are through formation of clouds & outgoing long wave radiation.
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Inversion:
- Subsidence inversion is caused by an old pressure system.
- A val ey inversion happens when cool dense air descends down valley slopes into basin.
- Main cause of terrestrial radiation is a cloud-free night in winter when the ground is dry. In winter, the ground
is colder than in summer, conduction cools the air above.
- Found commonly in stratosphere
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Diurnal variation:
- Highest temperature 2 hours after noon, lowest temperature half hour after sunrise.
- Highest diurnal variations: Deserts. Hot during day, cold at night.
- Lowest diurnal variations: Tropical areas.
- Variation is highest when sky clear & winds are weak.
- Variation bigger over larger land masses compared to the sea/other regions
- Wind increases difference in temperature between surface and 4ft (Mixing)
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Specific heat capacity:
- Amount of heat per unit mass required to raise the temperature by 1°C, i.e. higher specific heat = takes more time
to heat up
- Water has higher specific heat than land
- Grass less SH than concrete
- Rocks very low SH
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Isotherms: Tropical = 16000ft, Temperate = 6000ft, Polar = 0ft
Pressure
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Amount of pressure decreasing with height, lessens with height/smaller at higher levels/larger at lower layers.
E.g. MSL 27ft/hPa, 18000ft/5.5km 50ft/hPa
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Rate of pressure decrease with height is greater in cold air (More compact vertical isobars)
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QFF: Current pressure at aerodrome converted to MSL & actual conditions, used in weather charts
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Isobars: Lines of equal pressure reduced to sea level, lines of equal QFF, same air pressure at given level
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Isohypse: True altitude of a pressure level
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Contour heights: True heights AMSL
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“LOW”: Area of low pressure compared to horizontal environments and “high” Vice versa
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SEE positive & negatives
If height is ABOVE MSL (+) and Temp is > ISA (+) then QNH > QFF
If height is BELOW MSL (-) and Temp is < ISA (-) then QNH > QFF
If height is ABOVE MSL (+) and Temp is < ISA (-) then QFF > QNH
If height is BELOW MSL (-) and Temp is > ISA (+) then QFF > QNH
AT MSL QFF is always = QNH = QFF
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5 triple 1, 2 triple 3 & 4. 876543221
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Change in height H = 96 x T ÷ P, (Temp decrease, pressure increase to make isobars closer together)

Density
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Inversely proportional to temperature
Directly proportional to pressure
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There is lesser pressure & density in upper levels (Logic)
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Density = Pressure/constant x temperature
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Affected by altitude, temp & amount of water vapour
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High density altitude = low performance
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Density altitude: Altitude in standard atmosphere to which observed density corresponds

ICAO ISA
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Tropopause height: 36000ft, 11km, -56.5°C
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1m = 3.28ft
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1°C /2000ft & 0.65°C/100m

Altimetry
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Q-codes
- QFE: (Height) = Atmospheric pressure at the official aerodrome elevation
- QFF: QFE reduced to MSL according to actual conditions
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QNH:
1. Atmospheric pressure/QFE reduced to MSL using the values of the standard temperature/standard
temperature gradient
2. QNH = QFE + AD elevation in hPa
3. Difference between QNH & QFE is always the same
4. When airport is below MSL, QFE is always more than QNH
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TA: Transition altitude, altitude at which we refer vertical position in terms of altitude based on QNH
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TL: Transition level, lowest usable flight level
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ISA deviation negative = air is colder = true altitude less than indicated
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Always do pressure correction before temp correction then, determine if flying to lower or higher pressure
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4% for every 10°C deviation always applied to true altitude OR height above the elevation
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1 inch – 1000ft
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Pressure altimeter: Indicates altitude corresponding to difference between reference pressure & the pressure
where the instrument is. The distance between two isobaric surfaces in the standard atmosphere
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Best conditions for flight level to clear all obstacles: Temp >/= ISA, QNH > 1013
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To find lowest usable flight level from a MSA, Get lowest QNH and highest negative temperature
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To assume whether air mass is colder or warmer: Look at either given pressure or temperature
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Temperature correction must be done using the height from the station where the altimeter starts measuring
from