PPL MET Flashcards
Atmosphere Divisions
Nitrogen
Oxygen Other gases
78%
20%
2%
Troposphere
Temp decreases with height 2*/1000 15*C --> -56.5*C top Temperature based on ISA All weather occurs Lapse rate (temperature decrease) stops or stay constant
Tropopause
- isothermal lapse rate
- cloud
- high cloud tops
Stratophere
- temperature increase with height due to ozone layer
- temperature inversions
- -56.5 at stratospause
Stratopause
- similar to tropopause
- temp lapse rate pauses + stay constant
- negative lapse rate
Conduction Convection Radiation Advection Latent heat
- 2 touching particles will transfer heat between each other
- heated particles will rise allowing cooler particle to sink
- transfer of electromagnetic waves (solar + terrestrial )
- horizontal movement of air masses
- absorption + release of heat energy through evaporation, freezing + condensing
DALR
SALR
3/1000
1.5/1000
Saturation
100% filled with water = reached saturation
a particle is saturated - cloud
100% humidity
water vapour condenses into visible moisture (latent released to environment)
Relative Humidity
- amount of water in a particle compared to amount possible
Humidity = vapour present / vapor possible x 100 - how close to saturation or 100% a particle is
Dew Point Temperature
to reach 100% humidity
The greater the water present =
- constant amount of water vapour present
- particle cooled until it reaches the dew point tempreature
- as it rises it cools until it reaches DPT + cloud forms - kept a constant temperature
water vapour is added until it reaches 100% humidity
= the higher/warmer the dew point
Stability
parcel of air is the same temperature as it surrounding environment + will be minimal vertical movement
- cloud form in a stable atmosphere there must be lifting mech
Unstable
- when a parcel of air is warmer than its surrounding environment + continues to rise
Cumuliform
- produced in an unstable atmosphere
- by rising convective air
- cumliform clouds are heaped or towering in appearance
Stratiform
- produced by stable conditions
- flat and layered in appearance
Low level ___ft
Mid Lvel ___ft
High level___ft
7-8000ft
7-8000 to 20000ft
20,000ft and higher
Cirrus
- high level cloud
- white + fibrous
- composed mainly of ice crystal
Cirrocumulus
- high level cloud
- thin + sheet-like, covering the whole sky (hale effect)
- ice crystal
Altocumulus
- mid level cloud
- white or grey layer in arranged dump
- water droplet + super cooled water droplet
Altostratus
- mid level cloud
- grey/bluish layer, often covering all of the sky (halo effect)
- water droplet, supercooled water droplet + ice crystal
Nimbostratus
- low or mid level cloud
- grey, dark grey
- continous snow or rain
- water droplet - heavy continous rain
Stratocumulus
- low level cloud
- grey / whitish layer with darker elements
- water droplet
Stratus
- low level cloud
- grey layered cloud with a uniform base
- water droplet
Cumulus
- low level cloud
- detached with sharp outlines, like rising mounds
- water droplets, larger with supercooled water droplets
Cumulonimbus
- low level cloud
- heavy + dense with great vertical growth(thunderstorm)
- water droplet + supercooled water droplet
Low pressure System
- clockwise in the southern hemisphere (AC in Northern)
- airflows converges at the surface + rises
- most unstable + brings adverse weather
Coriolois Force can be increased with
more mass+ density mass
High pressure
- anti-clockwise in Southern(C nothern)
- air subsides down towards the surface then spreads out
- stable conditions
Coriolis force
- earth’s rotation
- southern hemisphere = as particle moves north its path over the earths is deflected left
- earth rotating west to east
- closer to equator = coriolis force decreases
- at equator = zero
- closer to ground the coriolis decreas due to surface friction
Wind gradient
- main cause of surface wind is local pressure changes
- circulat patterns with high and low pressure are due to pressure gradient
- closer the isobars are the the greater the pressure gradient and wind speed
Buys ballot law
- his back to the wind in the souther hemisphere
- lowest pressure will always be on his right hand
Backing
- anticlockwise direction (observer turns to his left I continue facing the wind)
Veering
- clockwise direction (observer turns to his right to continue facing it)
Surface Friction
- 3000ft
- below this layer the wind speed + direction changes due to the friction caused by the earth’s surface
- over land: wind veer by 30*C and speed decrease by 2/3
- over seas: wind veer by 10*C and speed decrease by 1/3
gradient flow
weaker/stronger than coriolis
weaker = left flow (high pressure) stonger = right flow (low pressure)
geostrophic
isobars are straight
balance
constant speed along straight isobars
Gust
rapid increase then fill in wind speed
Squalls
wind changes in at least 16kts to reach 22kts for at least 1min
Land breeze
- coastal regions
- night the land cools much quicker than the sea
- produces a pressure gradient due to the temperature differential
- greater the temperature differential the stronger the wing
- lighter than sea breeze
Sea breezes
- coastal region
- differential heating between land and sea
- summer or hot days
- sea is poor conductor of heat
- afternoon the land becomes warmer compared to the ocean
- greater the temeprature difference the stronger the winds
- 3pm
katabatic winds
- forming in the evening, flowing down slopes or hills
- land loosing heat at night due to terrestial radiation
- strongest on cloudless night
- cold, dense air slides down mountains
- light
Anabatic Winds
- during the day
- ground is heated up
- hot air rises
- weaker than katabatic wind
Fohn Wind
- humid air is forced up over a mountain
- as it rises cools adiabatically to reach its dew point
- cloud is formed
- latent heat is released
- warm dry air flows down the lee side
- cloud base will be higher on windward side
How are fronts formed
- air masses move and encounter air of differing temp
- air have different densities very little mixing between air masses
Cold Fronts
- heavier air + dense + slides underneath warm air
- cold air advances its force warm air to rise forming a cold front
- air that is forced to rise is unstable + produces unstable conditions
Frontal Approach of cold front
- wind speeds increase to 15-50kts
- wind north-north westernly
- temperature increase + pressure decreases
- cumulus. Cumulusnimbus, rain
Cold front Passage
- wind back to south/west
- temp falls + pressure rises
- humidity rises
- thunderstorms or squalls, low clouds
Warm Fronts
- cold air retreats and warm air occupies previous position
- warm air is still forced to rise over heavier cold air = warm front
- stable = cirrus/cirrostratus/all weather
- cloud then will thicken and lower
- nimbostratus = heavy continous rain
- warm air now overing over cold ground = very stable
Warm front Approach
- wind speed 20kts
- cloud developing well ahead of front thickening
- wind from the north-east
- pressure falls
- rain beginning well ahead of front
Warm Front Passage
- wind backs to north-west
- rain eases then stops
- cloud clears to south-east
- Temp starts to rise
- Humidity increases + pressure steadies
occluded fronts
- cloud fronts travel faster than warm fronts
- cold front can overtake a warm front
- warm front travels clockwise around a low pressure cold front + cold front can catch up to the warm front
- features both weather from cold and warm
Stable
Unstable
Conditionally Unstable
DALR>SALR or ELR = stable
ELR > DALR or SALR = Un-stable
DALR> ELR or SALR = Conditionally un-stable
Fog
Formation of fog
Clearing of Fog
- cloud on the ground
- vis reduced below 1000m
1. clear skies at night
2. light winds
3. humid air - increase wind strength
- increase solar heating
- lift to low stratus cloud
- thicken due to mixing then will start to lift or dissipate
Mist
- vis is 1000m or greater
Radiation Fog
- forms over land during evening or early morning
- at night earth loses heat due to terrestrial radiation
- air above ground is cooled by conduction
- if air is moist its cools to its dewpoint + fog forms
Advection Fog
- Horizontal passage of warm moist air over a cold surface
- moist air is cooled down to dewpoint
- found over the sea or coastal regions
- during night or day
Inversions
- temperature decreases with height in the trospophere
- warmer layers of air can sit above cooler layers
- temperature inversions - temperature is increasing with height
- convections limited to below the inversion layer (trapped by warm air above)
- inversions stable conditions
Inversion conditions
- below inversion layer - port vis + bumpy conditions
- above inversion layers - good vis + smooth flying conditions
Radiation Inversion
- common type of inversions
- forms on the earths surface night
- at night - ground cools due to terrestial radiation
- air is poor conductor = limited to a fairly this layer + air above is virutally unaffected
Cold Air
- moves into a region occupied by warm air
- cold air is denser and slide sin underneath warm air
- warm air now sits above cold - inversions
- local surface heating can cause cold air to heat and rise
- if above warmer parcel is warmer than rising air, convection ceases
- visibility is reduced and bumpy conditions below the inversion layer
Subsidence layer
- inversion formed in a high pressure system
- air is a high pressure system subside (it sink its spread out, diverges)
- as it fails the sinking air warms adibatically above the diverging air
- subsidence inversions form over summer in the subtropical ridge
Low level jet stream
- high pressure system to the west
- mountain range
- inversion layer
- morning (6-9am)
- high wind speeds found a low level in early hours of morning (up to 50kts)
- form when surface inversions are the strongest
- inversions shields the winds from the frictional forces of the terrain
Dust devil
- unstable conditions
- small scale swirling cloud of dust
- reduced vis
- cloud cause windscreen abrasion
Turbulence
- sun heating up the ground
- ground heats up the air and the air rises
- convective turbulence can be found underneath and within the cloud
- cloud may form (depending on moisture)
- convective turbulence will be strongest on hot summer days
Mechanical Turbulence
- created by wind flowing around building, rough terrain, trees
- strong wind
mountain waves
- strong winds blows at right angles to mountain ranges
- mountains creates barrier and the wind starts to undulate
- create severe turbulence + aircraft is hard to control
- stability - stable layer at height of the mountain unstable underneath and less stable layer above
Lenticular clouds
- form in the crests of the mountain waves and are less shaped
- rotor clouds from in the rotor zone found under lenticular clouds
hoar Frost
- cruising at high altitudes for long period of time
- airframe cools to same temperature as surrounding air (cold soaked)
- aircraft descend into the humdi air
- humid air contacts a/c and freezes
Freezing Rain
- flying above the freezing level
- skin gets below zero
- flying through rain can freeze on contact
Icing - super cooled water droplets
3 factors to form ice
- they will not connect if they are already frozen
- small supercooled water droplets from Rime ice
- larger super cooled water droplet from clear ice
1. Temperature
2. cloud type
3. droplet size
Rime Ice
0* to -15
- small supercooled droplet, freeze instantly created a mixture of tiny particles with trapped air
- makes the ice brittle and white
Clear Ice
-10* to -39*
larger super cooled water droplet takes longer to freeze when on a/c surface
Frost
forms on a/c surface over night
- disrupt airflow, increase stall speed, TODR
- must removed before flight
Windshear/downburst
- change in wind speed and direction with a change in height
- downdraught from a thunderstorm - presence can be indicated by blowing dust at the surface or viagra
- most severe turbulence from downdraught associated with thunderstorms after mature stage
Thunderstorms Development
- high humidity
- atmosphere stability
- trigger mechanism
Cumulus Stage
growing or formative stage
- last up to 30 mins
- stage is with updraught
Mature Stage
- updraught can no longer support rain drops
- downdraught begin to form and rain is released from the cloud
Dissipating stage
- only downdraught
- storm is starting to fall apart
- 30 mins
Thunderstorm triggers
heat or convection -hot air rising in an unstable atmosphere
frontal = air forced to rise
Cold Stream - cold air stream that moves into a warmer environment (latitudinal hearing)
- does not rely on direct solar heating
Nocturnal Thunderstorms
- ocean retains its heating helping the bottom of the - cloud stay warm
- tops of cloud lose heat to atmosphere
- increase instability the cloud
orthographic thunderstorms
- mountain cause air to be lifted to trigger thunderstorms
Thunderstorm hazards
- turbulence and windshear
low level windshear (thunderstorm hazards)
- downdraught from the thunderstorm spread outwards at low level create gust fronts
- sudden change in wind speed and direction
hail (thunderstorm hazards)
- cause serious damage to a/c
- middle of the cloud
- clear air underneath the cirrus anvil
Lightining (thunderstorm hazards)
- damage vis when flying in heavy precipitation is hazard to VFR a/c
VIS (thunderstorm hazard)
-Reduced vis when flying in heavy precipitation is hazard to VFR a/c
Viagra
- rain evaporates before hitting the ground
- indication of downdraught/mirco burst
Tropical Cyclone Conditions
- small and intense low pressure system
- over warm ocean
Tropical Cyclone
- formative stage the centre of pressure is steadily dropping violent winds
- pressure been falling, temperature is rising
- central temperature risies above the dew point temperature creates the ete as the cloud no longer exists in centre
- depression stage if the cyclone moves out of 5S and 15S (marked by torrential rain and flooding)
