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THE

PILOT

meteorology
ATPL
STUDENT
pilot
resume

all info you need to pass atpl exams

Tropopause/Troposphere
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Meteorology

Troposphere
- Concerns aviators
Tropopause
- Mid-latitudes ISA: 11km & -56
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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
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clear nights = colder
The main methods of heat transfer are through formation of clouds & outgoing long wave radiation
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A valley inversion happens when cool dense air descends down valley slopes into basin
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In winter, the ground
is colder than in summer, conduction cools the air above
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Highest diurnal variations: Deserts
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Lowest diurnal variations: Tropical areas
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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
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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
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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
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5°C
1m = 3
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65°C/100m

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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
QNH:
1
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QNH = QFE + AD elevation in hPa
3
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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
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Strongest winds are between two air
masses
Cup anemometer measures wind speed at 8-10m AGL
Km/h = (knots x 2) - 10%
Knots = [(km/h) ÷ 2] + 10%
Veers: clockwise, backs: anticlockwise

Cause of winds:

Primary – Difference in TEMPERATURE
Horizontal pressure difference:
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Geostrophic wind:
Parallel to straight isobars, perpendicular/right angles to & balanced with PGF & CF, Winds >2000ft no friction
Only exists above 15°N/S
Proportional to PGF
Inverse to CF (Earth’s rotation)
Inverse to latitude, higher latitude = more CF, wind speed less
Inverse to density
NO CENTRIFUGAL FORCE
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Gradient wind:
Parallel to curved isobars due to surface friction, PGF, CF & centrifugal force
- Decreases with increase of latitude
- Gradient wind is higher than geostrophic wind around a high
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Centrifugal force opposes PGF
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PGF:
Force perpendicular across isobar towards LOW
- Proportional to pressure gradient
- Inverse to density
- PGF always acts from H to L pressure
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Coriolis force/earth’s rotation:
CF deflects wind to the right in N hemisphere, left in S hemisphere
Prevents wind from flowing directly H to L
Northern hemisphere: CCW HI, CW LO
Southern hemisphere: CW HI, CCW LO
Coriolis force decreases with latitude
Coriolis force decreases with decreasing wind speed
0 - 10° N & S CF negligible
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Surface winds:
<2000ft (Friction layer) deflected due to coriolis force, blows across isobar, convergence and deflection caused
by friction which decreases wind speed & causes direction change
- Backing northern hemisphere
- Veering southern hemisphere
- Land 50% 30°, sea 70% 10°
- Friction layer:
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Time of day: Strongest at mid-afternoon, weakest at night
3
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Type of surface
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Cyclones(Low):
Convergence caused by frictional forces & cyclonic curvature of the isobars
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Anticyclones(High):
At same distance between isobars, any latitude: V Low < V straight < V High
Blocking/warm anticyclone has inversion layer near surface which is colder than upper air, thus increased
performance
Warm anticyclone over land in summer has fine weather, it increases intensity with altitude
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Errors: Isallobaric effect, when pressure is changing rapidly

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Diagram: Feathers point to lower pressure value

Local winds

Land & sea breeze:
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Due to diurnal variations, slack pressure gradient, higher land temperatures due to clear skies, pressure at
higher levels increasing, land surface cools & heats faster than sea:
- Wind sea to land during the day, 1000 – 3000ft 10kts
- Land to sea during the night, 1000ft 5kts (Weaker)
Mountain winds
- Downslope/Mountain wind: Katabatic at night, (Kata –cold, gets warmer and dryer as it descends)
- Upslope/Valley wind: Anabatic during day
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Due to venturi effect when passing through valley there is a low pressure, causing a drop in static pressure and
an apparent increase of indicated altitude, actual altitude is lower
Mountain/standing/lee waves
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Conditions for formation:
- Wind speed more than 20kts, turbulence downwind side of range
- Wind blows at right angles to the mountain range or within 30°
- Wind speed increases with altitude up to tropopause but does not change direction
- Stable atmosphere, less stable above and below/inversion just above the crest
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Creates altocumulus lenticularis (Lens), rotor & cap clouds
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Air’s ability to hold water increases
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When parcel of air descends
4
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Air’s ability to hold water vapour decreases
2
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As parcel of air ascends
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Also modifies lapse rate of parcel from DALR to SALR, moving it vertically
Air parcel ascended will stay level when it is the same temperature as environment
Temp of air parcel lower than environment = Air sinks as it has higher density = Stable
Temp of air parcel higher than environment = Air continues to rise = Unstable
After turbulent mixing, unsaturated air remains at DALR
Even ascending at isothermal layers, unsaturated air cools at DALR
ELR = 2°C/1000ft or 0
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8°C/1000ft or 0
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Stratus:
Uniform base and uniform appearance
Give drizzle or snow grains
The outline is clear
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Nimbostratus:
Continuous falling rain or snow
Grey often dark
Reach the ground
Block out the sun
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Altocumulus lenticularis: Indicates mountain waves
Pebble or cylindric form
Never touches the ground
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Towering cumulus congestus
Sprouting vertical extent
Bulging upper part like a cauliflower
Temperature in the cloud higher than ambient
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Castellanus cumulonimbus:
Turrets
Taller than they are wide
Seem to be arranged in line
Heights:
Low: 0 – 6500ft
Medium: 6500 – 23000ft
High: 16500 – 45000ft
Stratus: Stratified clouds indicate stability
Formed via radiation during the night from the earth surface in moderate wind
Formed via turbulence when in the friction layer mixing occurs due to turbulence & condensation level is above
top of turbulent layer
Dissipated through insolation (As temperature increases due to sun’s heat), which lifts condensation levels\

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Temperature nearly similar to surroundings
Cumulus:
Indicates up & downdraughts
Top of clouds are limited due to inversion
Large water drops, instability, turbulence, showers & clear ice
Fair weather cumulus: Heating of land surface by day in a stable atmosphere, indicates turbulence at and
below cloud level
Temperature higher than surroundings, warm air rapidly rising to cooler air above
Turbulence cloud is created as a result of mixing from turbulence
Orographic clouds: Air forced up a mountain reaches dew point with height, creating clouds
Polar maritime air at night moving over northwest Europe decreases cloud amount (No convection) and lowers
cloud base (Cloud base formula)
Cirrostratus gives HALO
Advection can form fog (advection fog) & clouds (warm/cold fronts)

Fog
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Radiation fog: Vertical
Only on land, after sunrise
Clear sky for terrestrial radiation, heat loss from the ground on clear nights
High humidity, high pressure areas with calm very light winds <5kts
Dissipates and forms stratus with increasing wind speed & insolation
Up to 500ft
Advection fog: Horizontal
Ground cooling due to radiation
Cold surface: Temp of surface lower than air moving over it
Wind speed up to 20kts sea & 15kts over land
Humid air, clears by changing air mass
Cold sea current e
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Labrador, during spring in Newfoundland
Warm air moves over cold land, crating fog, winds get stronger and mixing of the air creates stratus, which are
turbulence clouds
Steam/artic fog
Cold air mass moving over warm water surface
No wind
Orographic/hill fog:
Day/night fog
Air forced upslope or downslope katabatic wind flowing down a valley cools till dew point
High relative humidity air forced up a hill/mountain
Dissipates with a change of airflow direction
Frontal fog:
Due to evaporation & condensation of warm falling precipitation into cold moist layer ahead of warm front
Very humid warm air meets very humid cold air
Condensation of air saturated by evaporation of precipitation
Forms at day/night in a narrow band where frontal surface meets the ground
Dissipates after passage
Visibility
Fog: <1000m
Mist: ≥1000m but <5000m
Haze: Smoke/Dust/Sand ≤5000m
Other fogs
Shallow fog depth: 2m land & 10m water
Freezing fog: Supercooled water droplets
Dissipation of fog/lifting to low stratus:
Surface heating
Wind speed increasing

Development of precipitation
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Bergeron-Findeison(Ice crystal) process:
Saturation vapour pressure over water is greater than on ice
Takes place in clouds with only ice crystals & supercooled water droplets which warms and falls as rain
At high levels in a cloud some water droplets turn to ice & grow by sublimation
Happens in mixed phased clouds
Coalescence
Merging of two or more water droplets, when droplets get to large they fall as rain
At mid latitude this process only produces drizzle
Upward currents increase growth rate of precipitation due to collision of water droplets
Conditions for freezing rain:
Surface temperature <0°C
Temperature inversions with warm air aloft falling into air below 0°C
Ahead of warm fronts or occlusions with continuous precipitation

Precipitation types
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Light, moderate or heavy
Drizzle:
0
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5mm small water droplets
Falls from clouds only containing water such as ST/SC
CB clouds, convective clouds:
Hail/grail (GR): In continental regions in mid-latitudes, large hail associated with severe thunderstorms
Rain showers, hail showers
Ice pellets: Frozen precipitation
Translucent/transparent freezing of raindrops bouncing of surfaces <5mm
Indicates freezing rain at higher levels
Freezing rain/supercooled water droplets:
Liquid form, forms in clouds, fog precipitation
Small droplets: Rime ice, freeze immediately
Large droplets: Clear ice, Partially freeze on impact, remaining part flows back along surface & freeze
Snow grains:
< 1mm white opaque
Falls from stratus or supercooled fog
Snow: Biggest impact on visibility
Virga: Streaks of precipitation, water or ice particles evaporating before reaching the ground
After a rain shower passes an airfield, air temperature drops and dew point rises, as cold air from above
reaches ground & humidity content rises

Air masses
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It is an extensive body of air within which the temperature
Properties obtained from pressure system & characteristics of source
Polar continental air has lowest temperatures
Tropical continental air originates from Balkans, near east & Siberian landmass
Europe:
Western: Polar & tropical maritime
Northern/Scandinavia: Polar maritime & polar continental
South/Mediterranean: Tropical maritime & tropical continental
Cold air mass:
Unstable giving showers
Gusty winds & good visibility
Warm air mass:
Stable, cooling from below
Continuous rain & poor visibility
Warm sector:
Visibility 5 – 10km

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Basic facts:
Interval between frontal waves: 1 - 2 days
Summer: NE Canada Newfoundland to N Scotland
Winter: Florida to SW England
Upper winds blowing across fronts make it move faster
Direction of frontal depressions are in the direction of warm sector isobars
Surface winds veer & upper winds back
Transition zone between two air masses creates a frontal low pressure
Generally caused by temperature contrast between artic air & equatorial air
Wind directions: Behind cold: NW, In front of cold : W, in front of warm: South, North of centre of low: East
Warm front:
Risk of fog greater ahead & behind compared to cold front
CI announce arrival, Halo effect
1:100 – 150
TS forms when warm air is unstable
FZRA in just in front of surface position of warm front may cause clear ice accretion
Surface position may have windshear
Velocity: 2/3 speed of measured distance between isobars
Stratus/cumulus fractus clouds exists in warm or cold front
Reason for very low clouds ahead of warm front:
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Rain drags warm air into cold air and condenses it
Pressure
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At passage: At lowest point
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Before: Decrease (Pressure decrease indicates a climb on altimeter)
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After: Steady increase
Occluded warm:
Warmer air behind front
On surface charts extension of warm front
Usually in winter
Ahead of warm occlusion: Low level ST clouds
Occluded cold:
Colder air behind front
On surface charts extension of cold front
Usually in summer
Stationary front:
No horizontal motion perpendicular to front
Surface wind parallel to front
Warm sector:
Tropical air
Moderate to good visibility, haze & few or scattered cumulus, drizzle, no high level clouds
Poor visibility at lower levels possible advection fog, mist & drizzle
Summer: Fair weather CU
Winter: ST & SC broken to overcast, poor visibility in mist & drizzle
Generally stable VMC conditions above ST & SC clouds

Pressure systems:

Main lows:
Winter: Iceland/Greenland
Summer: North Canada
Main anticyclones:
Winter: Azores, Siberia, Canada, South Pacific
Summer: Azores, SE USA, SW Europe
Sub-tropical highs exist on 30°N
Anticyclones:
Principle of divergence(At surface) & subsidence(Sinking), as air sinks it is heated by compression, sinking dry
air and producing inversions, fog and low ST
Stable layer at an old high pressure system creates dry air and a subsidence inversion
Cold high pressure:
1
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May weaken at altitude & change to low pressure
Calm winds & haze
Blocking anti-cyclone: Quasi stationary, warm anticyclone, converts normal W –E movements to meridional
Cold temporary anti-cyclone: Found between two frontal depressions
Thermal & dynamic depressions/lows:
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Low pressure areas: Convergence with lifting air mass
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Thermal warm low pressure areas:
Surface of the earth is warmer than the air over land in summer, may occur on water in winter
Temperature rise in an area in relation to the environment
Weakens with increase in height and may turn into a high
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Dynamic cold low pressure area:
Low strengthens when temperature difference increase in winter, increase with increase in height
Air centre of low pressure area colder than surroundings, example Icelandic low
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Polar/instability lows:
Cold polar/artic air moving SE over warmer seas, forming only at sea in winter
Low pressure receiving energy from released condensation heat
Short wave disturbances along the polar front
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Secondary depressions/lows:
Moves anticlockwise/cyclonic around the main in N hemisphere
Formed at cold fronts

Tropical revolving storms
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Caused via latent heat released from condensing water vapour, main source of energy
Occurs in late summer or early autumn and decays upon reaching landmass
Diameter of the eye: 10 – 20NM, Diameter of whole TRS: 270NM, DENSE CI indicates TRS
Has the highest cloud tops among other weather phenomena
Most dangerous zone in TRS: Wall of clouds around the eye, greatest wind speeds
The eye: Extends from surface to top/troposphere, air is <63 knots & descending, warmer than surroundings
Most dangerous TRS: South China Sea & Philippines
Most frequent TRS are typhoons: North West Pacific, Japan, China & Taiwan
Disturbance, depression, storm, severe storm, revolving storm
TRS forms on western part of tropical oceans as trade winds bring humidity as it blows along sea passage
Cyclones form at: Caribbean sea, Gulf of Bengal & Indian ocean east of Madagascar
Cyclones do not form at the South Atlantic or South Pacific ocean because of low water temperature
Hurricanes in North Atlantic:
Eye can be observed by satellites
Move parallel & away from equator
Speed >64 knots
Caribbean area, moves west and turns north east, towards US SE coast
To form: Surface temperature > 27°C, 5 - 15° away from the equator

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Locations:
East Darwin: 2
West Darwin: 5
Atlantic: 6
Philippines: 9
Bay of Bengal: 12
Time of year
Hurricane: US=JUNO
Typhoon: SE-ASIA=JUNO
Cyclones:
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ARABIAN SEA=MANOV
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BAY OF BENGAL=JUNO
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AFRICA(South of Indian ocean)=DECAP
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PACIFIC=DECAP
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DARWIN=DECAP
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Climate zones:

Zones Poles to equator:
1) Polar high: Mean temperature of all months below +10°C, high pressure weather dominates with the subsoil being frozen
2) Disturbed temperate low (40° – 60°) for coastal areas: Chilly summers & warm winters
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After melting it should increase again
At low OAT to dew point spread
Subject
Clear
Rime
Mixed
Others
CU/CB/Thunderstorms 0°C to - 23°C -10°C to 30°C (Top) -17°C to -23°C
NS
0°C to - 10°C
-7°C to -13°C
-7°C to -13°C
ST/SC/AS
0°C to -15°C
Hoar frost on airframe
-15°C
Carburettor
RH>30%, Min -5°C Max 30°C

Turbulence & wind shear:
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CAT:
Avoided by changing flight level, usually descend as reported jetstreams have a thick layer
When experienced: Maintain wings & control pitch smoothly, decrease speed/climb/descend above zone
CAT Levels
Moderate: Moderate altitude/attitude changes, small variations in airspeed strain on seat belts, unsecured
objects dislodged, walking difficult but aircraft remains in positive control at all times
Severe: Abrupt altitude/attitude changes, aircraft out of control short periods, accelerometer > 1g, loose
objects tossed about, can cause damage, unpleasant
Windshear:
Expressed in kt/100ft
A vertical/horizontal wind velocity/direction variation over a short distance & limited period of time
Is a type of CAT that is proportional to intensity of the windshear
Low level temperature inversions, is greatest at the top of a marked surface based inversion, associated with
radiation inversions
Vertical windshear: Vertical variation in horizontal wind, change of horizontal wind direction/speed with height
Effect of windshear/gust on aircraft:
Tailwind increase: Airspeed decreases, as a result low airspeed = lift decreases and rate of descent increases
Headwind increase: Airspeed increases, as a result high airspeed = lift increases and rate of descent decreases
Intensity
Light = <4 kts/100ft
Moderate = 4 - 8 kts/100ft

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Strong = 8 - 12 kts/100ft
Severe = >12 kts/100ft

Thunderstorms:
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Lasts typically 2 hours, max height of CB = 20km, hail from ground up to FL450
AC Castellanus indicates upper level instability & possible thunderstorms, precedes thunderstorms
Most probable severe thunderstorm occurs when cold maritime air advects over warm sea surface
Conditions for formation:
1) Unstable air/conditional instability: ELR higher than SALR through a great vertical extent
2) Humidity: High relative humidity
3) Lifting action(Trigger): Initial lifting process
- Convection
- Advection
- Frontal uplift
- Orographic uplift
- Convergence of air associated with low pressures
- Intense insolation of a COL or weak low
Stages:
1) Initial:
- 15-20 mins
- Only updraughts
2) Mature:
- Greatest intensity, updraughts & downdraughts, rotor clouds
- 20 – 30 mins
- Below -23°C icing still possible
- Start of stage marked with start of precipitation
3) Dissipating:
- Well-developed anvil can be seen, only downdraughts
- 30 mins – 3 hours
Lightning:
When flying through electrically charged air the aircraft in itself may carry charge & trigger lightning discharge
When lightning strikes the aircraft is temporarily part of the trajectory
Stormscope: On board instrument to measure electrical discharge
Example: St Elmo’s Fire
Leads to disorientation, temporary difficulty in determining attitude of flight
If aircraft was made of composites, severe damage occurs, crew may be blinded & temporarily lose hearing
Radar reflection reflectivity:
Increases with severity & frequency of turbulence,
A function of number & size of water droplets in a given unit of volume
Air mass & frontal thunderstorms:
Main thunderstorms, most frequent in tropical areas
Air mass thunderstorms:
Isolated & develops in the afternoon over land in summer,
Due to convection/thermal triggering,
Most difficult to forecast or detect
Frontal thunderstorms:
Most difficult to avoid
Most fastest moving
Formed due to rising air in falling pressure at air mass boundaries
Warm front thunderstorm: When warm air is moist & ELR > SALR
Single cell thunderstorm:
Moves according to 700 hPa winds
Squall line thunderstorms:
Most destructive
Band/line of thunderstorms ahead of cold front
Supercell thunderstorms:
Requires lots of moisture & wind vector change aloft

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TS/CB avoidance criteria:
5000ft vertical separation
10NM without AWR, best to avoid but when necessary fly through the sides
Thunderstorm cells:
5NM GND – FL200
10NM FL200 – 250
15NM FL250 – 300
20NM Above FL300
Avoid flying under “Anvil” due to hail, lightning & severe turbulence
Microburst: Downdraught high speed lower temperature 4km in 5 mins, Typical – 50 knots, max – 100 knots
Macroburst: More than 4km, great change over a large area
Gust front:
Descending cold air undercutting warmer inflowing air
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Tornadoes

Diameter: 100 to 150 metres
Associated with CB clouds
Wind speeds over 200 knots
Movement speed 20 – 40 knots
Most likely occurs in spring & summer
West African Tornado (WAT): Squall line created by atmospheric waves
Life span up to 30 mins

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Inversions

Low level temperature inversions formed due to radiation cooling on clear nights, promotes windshear
Above inversion layer: Better visibility, reduced performance due to warmer air, stronger veering & wind speed
increase
Valley inversion: Radiation cooling + gravity

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Mountain waves
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Best time to fly over alps in summer on a hot day: Morning
Conditions:
Stable air, speed >25 kts blowing across ridge
Indicates strong wind & turbulence, may be accompanied by rotor/roll clouds or ragged altocumulus lenticularis
Rotors:
Upper part of wind flows in the same direction as wind, lower part in opposite direction
Exists on leeward side
A low-level phenomenon
Standing waves exist in vicinity of roll cloud or rotor zone beneath first wave
CAP clouds, seem harmless but brings downdraughts 5000ft/min
Flight headwind towards high ground (Towards leeward side of mountain) is more hazardous than tailwind
toward high ground (Approaching from windward side of mountain)
Clouds pushed up a mountain contain moderate to severe mixed ice
Out of phase with waves are nonsense

Visibility
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Depends on type of precipitation and intensity
Rank:
Blowing snow: 1 – 50m
Tropical downpour: Tens of metres
Heavy snow showers: 100m
Heavy snowfall: 50 – 200m
Drizzle: 500 – 300m
Fog: < 1000m
Heavy rain: < 1000m
Moderate snow: 1000m

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Mist: >1000m but <5000m
Moderate rain: 3000 – 5000m
Haze: <5000m
Visible moisture:
Cloud
Fog
Mist
Spray
Precipitation
Solid particles:
Atmospheric pollution
Dust
Sand
Volcanic ash
Haze: Formed due to solid particles, during sunset , sun is at a low position deteriorating conditions more
Unstable air: Showers of rain or snow
Low level inversions: Traps dust, smoke or other solid particles which makes moderate to poor visibility as there
is no vertical exchange

Observations:
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AWR:
Shows on plan position indicator the areas of precipitation of rain snow/or and hail
Accurate assessment of weather ahead may be hampered by attenuation of the radar echoes by heavy rain
Best way in dealing with thunderstorms in a cold front: Avoiding embedded CBs using AWR
Clear areas indicates no echoes being received, however radar provides no assurance of being in VMC in this
area
Most significant clouds: CBs & TCU
Atmospheric pressure: Mercury/aneroid barometer, recorded on a barograph
Humidity:
Hygrometer
Psychrometer: Compares dry bulb temperature with lowest temperature to which air is cooled by evaporation
of water
Dry & wet bulb thermometer
Surface temperature: Height of 2m, measures maximum, minimum, dry & wet bulb temperatures
Temperature & humidity aloft: Radiosondes
Radiosondes:
An instrument measuring meteorological variables provided with radio transmitter for sending to observation
station
Measures direct or indirect parameters e
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winds indirect, air temp, pressure & humidity direct
Surface wind measurement: Mast 10m above runway by cup anemometer connected to electrical anemograph
Gust: When wind deviates more than 10 knots of mean value, occurs less than a minute over a short distance
Squall: Sudden increase of wind speed at least 16 knots lasting for at least 1 minute
Horizontal visibility:
Determined by observer by means of marks/lights at known distances
Meteorological visibility on ground, used for VFR flight planning by MET office
Vertical visibility:
Used whenever the sky is obscured by fog or heavy precipitation & the height of the cloud base cannot be
measured
Flight visibility: Average visibility as seen from the cockpit
Runway visual range (RVR):
Length of runway a pilot would see when on the threshold
Visibility of RVR is generally greater than MET visibility
Determined by the use of forward scatter meters or transmissometers
Used when visibility decreases below 1500m
P: Plenty – Greater than
M: Minor – Lower than

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D: Down – Decreasing
U: Up - Increasing
N: Neutral – No change
V: Variable – Changing every minute
RVR represented on METAR is value representative of the touch down zone (TDZ)
Cloud coverage:
SKC: 0
FEW: 1 -2
SCT: 3 - 4
BKN: 5 - 7
OVC: 8
Cloud ceiling: Lowest cloud layer that covers half the sky below 20000ft
Cloud base: Reported in steps of 100ft up to 10000ft & 1000ft above 10000ft
Routine air report (AIREP)
Routine automatic report on weather conditions in flight
Air reports should be reported as soon as practicable
Special air report (PIREP)
Section 1: Position report: Aircraft ident, height, position & time
Section 3: Meteorological information
May trigger a SIGMET message
Satellites:
Used to locate fronts in areas with few observation stations
Pictures from polar orbiting satellites have better resolutions
Polar orbiting satellites, used to detect fog & cloud are closer to earth than geostationary satellites
To locate areas of fog, VIS & IR settings with polar orbiting satellites are used
Sources of meteorological information:
ATIS
VOLMET
All ATS units
Aeronautical Meteorological stations:
Makes actual observations at aerodromes and offshore platforms
Provides METAR & MET reports
World Meteorological Organization (WMO): Establish & implement together with ICAO a global regulatory
framework for national meteorological services
Meteorological watch office: Generates SIGMETs

Weather charts tips:
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Surface weather charts are weather forecast which is current, for time given on the chart, used to avoid areas
with turbulence, CAT & jetstreams
Line connecting places of the same temperature: Isotherm
Line connecting positions with same height of constant pressure: Isohypses, a number on the isohypses
represents topography height in decameters
Line connecting points of equal wind speeds: Isotachs
Lines on a contour chart joins points of equal height
When they ask for temperature, check the tropopause level
Tropopause in standard ISA is FL360 at 57°C
Wind speeds can be found by interpolation of wind information from two charts while considering maximum
wind information found on the significant weather chart
Find average temperature>>>Find flight level temperature
High pressure areas near maritime areas:
Summer low visibility, generally clear skies and possibility of afternoon thunderstorms due to heating
Mountainous area has orographic fog in relatively high pressures
Winter near hills/mountains near maritime area: Snow showers with gale force winds
Weather after cold front passage:
Pressure slow rise
Broken clouds CU/CB with heavy precipitation & possible thunderstorms
Stationary front: Red & blue

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Occluded front: Violet
Warm sector:
Constant temperature
Overcast with stratus or stratocumulus & drizzle, moderate to strong winds
CB clouds
Thunderstorm symbol implies moderate/severe turbulence/icing
ISOL: Individual CBs
OCNL: Well separated
FREQ: CBs with little or no separation
EMBD: Thunderstorm clouds contained in other clouds
Wind directions: Buy Ballot’s law, back to the wind, low pressure is on your left in Northern Hemisphere
Frontal passage NH wind veers, but anywhere else on the surface wind backs, speed determined by distance
between isobars

Information for flight planning
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METAR:
Every 30 mins, valid at time of observation
VC: Present weather within range of approx

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