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 t...
meteorology
ATPL
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pilot
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all info you need to pass atpl exams
, Meteorology
Tropopause/Troposphere
• Troposphere
- Concerns aviators
• 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
• Stratosphere
- Ozone contained
- Layer absolutely stable
- Lower part temperature constant
• Stratopause
- 50km
• Determining Tropopause height with formula: 16km (winter) or 18km (Summer) x cos latitude
Temperature
• 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
• 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.
• Inversion:
- Subsidence inversion is caused by an old pressure system.
- A valley 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
• 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)
• 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
• Isotherms: Tropical = 16000ft, Temperate = 6000ft, Polar = 0ft
, Pressure
• 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
• Rate of pressure decrease with height is greater in cold air (More compact vertical isobars)
• QFF: Current pressure at aerodrome converted to MSL & actual conditions, used in weather charts
• Isobars: Lines of equal pressure reduced to sea level, lines of equal QFF, same air pressure at given level
• Isohypse: True altitude of a pressure level
• Contour heights: True heights AMSL
• “LOW”: Area of low pressure compared to horizontal environments and “high” Vice versa
• 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
• 5 triple 1, 2 triple 3 & 4. 876543221
• Change in height H = 96 x T ÷ P, (Temp decrease, pressure increase to make isobars closer together)
Density
• Inversely proportional to temperature
Directly proportional to pressure
• There is lesser pressure & density in upper levels (Logic)
• Density = Pressure/constant x temperature
• Affected by altitude, temp & amount of water vapour
• High density altitude = low performance
• Density altitude: Altitude in standard atmosphere to which observed density corresponds
Altimetry
• Q-codes
- QFE: (Height) = Atmospheric pressure at the official aerodrome elevation
- QFF: QFE reduced to MSL according to actual conditions
- 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
• TA: Transition altitude, altitude at which we refer vertical position in terms of altitude based on QNH
• TL: Transition level, lowest usable flight level
• ISA deviation negative = air is colder = true altitude less than indicated
• Always do pressure correction before temp correction then, determine if flying to lower or higher pressure
• 4% for every 10°C deviation always applied to true altitude OR height above the elevation
• 1 inch – 1000ft
• 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
• Best conditions for flight level to clear all obstacles: Temp >/= ISA, QNH > 1013
• To find lowest usable flight level from a MSA, Get lowest QNH and highest negative temperature
• To assume whether air mass is colder or warmer: Look at either given pressure or temperature
• Temperature correction must be done using the height from the station where the altimeter starts measuring
from
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