Meteorology Flashcards
Approximately how much water is present in the tropopause?
0-5%
What is the percentage of gases in the atmosphere?
78% Nitrogen
21% Oxygen
1% other gases (argon, CO2, Neon, helium etc)
What is the height of the polar tropopause?
25000 feet
What is the height of the tropical/equator tropopause?
60000 feet
What changes to the height of the tropopause over summer?
Height will increase with increase of temperature
What is the ISA height of tropopause?
36090 feet
What is the temperature of the polar tropopause?
Approx -40 degrees
What is the temperature of the tropical/equator tropopause?
Approx -80 degrees
What is the ISA temperature of the tropopause?
-56.5 degrees
What happens to temperature in the stratosphere?
In lower layers temp is steady, increases near the top layer
Why does the temperature increase as we gain height in the stratosphere?
Due to the absorption of UV radiation and increase of ozone at higher levels
How high does the stratosphere go?
To 120000 feet
What is ozone and does it do?
Colourless, corrosive and irritating gas that absorbs UV rays, shielding humans from the damaging rays
What is the ISA pressure?
1013.25 hPa
What is the ISA temperature?
15 degrees
What does temperature decrease at?
1.98 degrees per 1000 ft up to 36090 feet
After 36090 feet, what happens to temperature according to ISA?
From 36090 to 65617 feet, temp is constant -56.5 degrees
After 65617 feet, what happens to temperature according to ISA?
From 65617 to 104987 feet, temp increases at 0.3 degrees per 1000 feet
Above what height will the ozone levels exceed humans tolerable limits?
50000 feet
What can be used to assist pilots break down ozone to an acceptable level?
Heat of compressor
What are the advantages of more dense air?
Lift required generated at lower speed
Greater engine power due to greater mass of fuel/air taken to cylinders
Breathing is easier
What happens to density and pressure as we gain height?
Pressure decreases, density decreases as number of molecules in cubic meter decreases
At what height is the density approximately half that at sea level?
18000 feet
At what rate does pressure fall?
1hPa per 30 feet (up to 5000ft AMSL)
Where is most of the mass of the atmosphere contained and why?
Near the surface due to gravity
What are the three ways heat can be transferred?
Radiation
Absorption
Conduction
Is air a good conductor of heat?
No
What is convection?
Mass of air is heated at the earths surface which will expand, become less dense and rise.
What is thermal convection?
Rising air carrying heat energy into atmosphere
What is advection?
Horizontal motion of air. AKA wind
What is ‘sea breeze’?
Solar radiation heating earths surface. Air in contact with surface becomes hot by conduction and rises. This creates low pressure over the land, and the high pressure from the sea will flow towards land
When is the sea breeze strength the greatest?
Mid afternoon on a hot day
What is land breeze?
During the night, earth surface cools by radiating heat into space. Earth surface cools quicker than the sea. (higher pressure over land and lower pressure over sea). Results in cooler air from land blows towards sea.
Which is generally stronger, land or sea breeze?
Sea breeze
What are katabatic winds?
Cool parcels of air sinking down the slopes of mountains
How do katabatic winds occur?
Earth surface cools through terrestrial radiation. Density becomes greater than lower air (more dense air is heavier) causes air to flow down slope due to gravity.
What are the ideal conditions for katabatic winds?
During night on a high plateau sloping steeply down towards low terrain (i.e. coast).
Clear skies over plateau
Relatively warm surrounding air
When are katabatic winds usually strongest?
Strongest at dawn
What are anabatic winds?
Winds blowing up sloping terrain
Why do anabatic winds occur?
Surface on slope heated and rises. Wind blows up to replace rising warm air.
Which is stronger, anabatic or katabatic winds?
Katabatic winds due to gravity
Where are anabatic winds likely to occur?
Westward slopes during summer afternoons
What are Fohn winds?
Warmer drier airflow on the leeside of the mountain
How are Fohn winds caused?
Highly moist air rising up mountain range having a high dew point temperature. If the air is cooled before reaching the top of the mountain, cloud forms on windward side. If precipitation occurs, moisture is removed from airflow causing air to be drier as cloud descends on lee side
What are low level jet streams?
High pressure circulating anti clockwise along Australian continent.
Crowds isobars together, increases surface pressure gradient causing wind speeds to increase
Freed of surface friction, gradient winds can reach what speeds at 2000 feet?
40-50 kts
Where are the greatest winds and when do they occur for low level jet streams?
West of great dividing range about dawn (0600 to 0900 LMT)
Which direction are low level jet streams usually from?
From south
What are the three states water exists?
Ice
Liquid
Vapour
In order from highest to lowest state, rank the water states.
Vapour
Liquid
Ice
Solid to liquid?
Melting
Liquid to vapour?
Evaporation
Solid to vapour?
Sublimation
Vapour to liquid?
Condensation
Liquid to solid?
Solidification
Vapour to solid?
Deposition
What is meant by the term ‘saturated’?
When amount of water vapour present is such that parcel of air is unable to hold more
How does change in temperature affect vapour state?
Decrease in temperature reduces ability to hold water in vapour state
What is relative humidity?
How close air is to saturation
Water vapour present in air to mass of water vapour which would cause saturation
What happens to the vapour possible as temperature is decreased?
It decreases
What happens at 100% humidity?
You have reached your dew point temperature
What is dew point temperature?
Temperature at which saturation occurs
What is the environmental lapse rate?
Temperature drop of 2 degrees / 1000 feet
What does the ELR determine?
Stability
How is a cloud formed?
When a parcel of air is cooled to its dew point temperature.
What is the dry adiabatic lapse rate?
3 degrees / 1000 feet.
Rate at which parcel of dry air cools as it ascends
What is saturated adiabatic lapse rate?
1.5 degrees / 1000 feet
What conditions are associated with a low ELR?
Stable conditions
What conditions are associated with a high ELR?
Unstable conditions
What are the conditions like in a stable environment?
ELR low High pressure system Stratiform clouds at high level Precipitation (if any) is steady Poor visibility Smooth conditions Little to no turbulence
What are conditions like in an unstable environment?
ELR high Low pressure system/trough Warm air continues to rise Turbulent (especially in thermals) Cumuliform clouds Showery rain if precipitation Good visibility inbetween showers
What happens to a parcel of air that is warmer than it’s surrounding environment?
Because it is less dense, will rise until encounters environment of same temperature
What happens to a parcel of air that is cooler than it’s surrounding environment?
Because it is more dense, it will sink until it encounters environment of same temperature
What are the triggers for vertical motion of air?
Convection
Orographic Uplift
Turbulence and Mixing
Frontal Uplift
What is convection?
Cold air going over a warm surface. The air is warmed from below and becomes less stable.
What happens in orographic uplift?
Humid air rises over mountain range, cools as gains height and rises. When dew point reaches clouds will form. As it descends, warms and dissipates
What is frontal uplift?
When cold and warm air meet, heavier cold air remains at the surface forcing lighter warmer air to rise over it
What is a front?
The boundary between cold and warm front
How are cumuliform clouds formed?
Formed by unstable warm air rising and cooling.
What are rain bearing clouds called?
Cumulonimbus
What temperature are stratiform/stratus clouds
Equal to or cooler than environment air
What is the base and tops for stratus clouds?
Base below 1000 feet and tops above 20000 feet
What are the high level clouds and what are their bases above?
Cirrocumulus
Cirrostratus
Cirrus
20000 feet
What are the medium level clouds and what are their bases between?
Altocumulus
Altostratus
Bases between 7500 and 20000 feet
What are low level clouds and what are their bases below?
Cumulus Stratus Stratocumulus Nimbostratus Cumulonimbus Bases below 7500 feet
What are cirrus clouds like?
High level with little turbulence and little to no icing risk
What are thin altostratus clouds like?
‘Bluish’ with little turbulence entering/leaving the cloud. Some rime ice and virga may be encountered
What are large cumulus (Cu) clouds like?
Low level ‘cauliflower’ shaped. Shower of rain, moderate to severe turbulence and a definite icing risk. Clear ice above freezing height
Describe cumulonimbus (Cb) clouds
Very large vertical extent with tops ‘anvil’ shaped.
What conditions are likely in cumulonimbus (Cb) clouds?
Thunderstorms, lightning, showers of rain, snow or hail.
Severe turbulence, violent entering/leaving
Definite icing risk
What is fog?
‘Cloud’ on ground
Visibility below 1000m
Nil turbulence or icing
Which clouds will there be ice present?
As, Ac Lenticularis and castellarius, Large Cu, Sc
Which clouds will produce moderate turbulence?
Ac lenticularius and castellarius, Cu, Cb, Sc
How long do individual showers usually last?
15-30 mins
What three conditions need to occur for a thunderstorm to happen?
Trigger
Instability
High humidity
What are the three stages of thunderstorms?
Growing
Mature
Dissipating
What happens in the growing stage of the thunderstorm?
Up-draughts up to 5000fpm
Water droplets carried higher and higher by up-draughts and can freeze if carried above freezing level.
How long does the growing stage last?
10-20 mins
What happens in the mature stage of the thunderstorm?
Up draughts and down draughts
Up draughts become weaker
Precipitation becomes too large for updraughts and rain commences.
extreme turbulence and windshear
How long does the mature stage last?
20-40 mins
What happens in the dissipating stage of the thunderstorm?
Cessation of updraughts
Cloud edges appear ragged and begin to evapourate
How long does the dissipating stage last?
30 mins
Does lightning pose a threat to flying?
Not to humans inside plane. May cause damage to radios and/or electronic equipment
At what height can hail occur during a storm?
10000-20000 feet
What is a microburst?
Short blast of cold air causing drastic change in vertical and horizontal wind speeds
What is an indicator that microburst may be present?
Virga
What is a tornado?
Rotating column of air from ground to base of a large Cu or Cb
What is a funnel cloud?
Tornado that doesn’t reach the ground
Is the central pressure higher or lower than surrounding air in a tornado?
Lower
How high can dust devils go?
Up to 7000 feet AGL
How long do dust devils last?
Less than 30 mins
How big in diameter are dust devils?
10-300 feet
If caught in a dust devil, what speed should you maintain?
Turbulence penetration speed
What is the worst kind of turbulence?
Frontal turbulence
Where do mountain waves occur?
On the Lee side of a mountain
What are the conditions for mountain waves to occur?
Lower half of troposphere
Mountain range greater than 1000 feet
Wind speed greater 25 knots at mountain top
Inversion or stable layer at the top
How should you avoid mountain waves?
In valley, keep downwind when air is rising
If lenticular clouds are present, fly upwind of them
What is the Runway Visual Range?
Maximum distance at takeoff or landing at which runway can be seen from position corresponding to average eye level of pilot at touchdown
How is the RVR derived?
Instrumentally derived
What is fog?
Very small water dropletts which reduce visibility to below 1000m
What is the relative humidity in fog?
Approx 100%
What temp can ice fog form?
-20degrees
What is mist?
Very small water droplets which reduce visibility to 1000m or more
What is relative humidity in mist?
Approx 95%
How is radiation fog formed?
Air cooled below dew point temperature, losing heat by radiation
What are the conditions required for radiation fog?
Cloudless night Cold land surface Moist air Small temperature/dewpoint High humidity Light winds (5-7 kts)
If the conditions are set for fog but the temperature is above freezing, what may occur?
Dew
If the conditions are set for fog but the temperature is below freezing, what may occur?
Frost
If the winds are above 7 knots but set for fog conditions, what may occur
Stratus clouds near ground
What is advection fog?
Warm moist air flowing across cold surface. If the temp is reduced to dew point, fog forms
Which is thicker/more persistent, advection or radiation fog?
Advection fog
What is upslope fog?
Moist air up a slope will cool adiabatically and if it cools below its dewpoint, fog forms
What happens if wind stops during upslope fog?
Fog disipates
What is an inversion?
Layer of atmosphere in which temperature increases with increase in height
What are the three common types of inversions?
Surface/radiation
Subsidence
Frontal
What is the conditions like in the lower layers of an inversion?
Smooth but poor visibility
How does radiation inversion form?
Forms at night by cooling of ground. Ground radiates heat to atmosphere and lower layers of air immediately cooled by absorption to ground
What conditions are required for radiation inversion?
Clear sky at night
Light wind
Suitable surface to promote radiation cooling
How deep can subsidence inversion be?
500 feet deep
What are the flying conditions like in an inversion?
Vertical windshear when climbing or descending through inversion
Gain thrust, lift and power descending into inversion
Turbulence
Cloud under inversion
Visibility better above layer
In summer, which direction does global circulation move?
Moves south
In winter, which direction does global circulation move?
Moves north
What direction does anticyclone move and what sort of system is it?
A high pressure system that moves anticlockwise
What is surface pressure?
Weight of air pressing down from above. When it cant descend any further it becomes divergent
What happens to air as it rises?
Reduction in surface pressure
Carries moist air with it
Expands and cools
What are low pressure systems, convergent or divergent?
Convergent
What do isobars join?
Equal pressure
What is a ridge?
Elongated finger of high pressure, wind turns sharply to the left
What is a trough?
Elongated finger of low pressure, wind turns sharply to the right
What is a col and what are the condition like?
Area between two highs and two lows. Conditions are light and variable
How does air move, low to high or high to low?
High to low
What is the rate of change of pressure?
Pressure gradient
What happens with a steeper pressure gradient?
Means winds are faster
What do closely spread isobars indicate?
Strong winds
low pressure
What do widely spread isobars indicate?
Light winds
High pressure
What direction does the pressure gradient act to the isobars?
Acts at right angle
Which has a greater rotational velocity, pole or equator?
Equator
Which direction does rotation velocity appear to turn in southern hemisphere?
To the left
What happens with a faster pressure gradient/airflow?
Coriolis force is stronger
Is there a coriolis force within 5 degrees of equator?
No
What happens when pressure gradient equals coriolis force?
Air flows parallel to isobars
Called geostrophic wind
Where will the wind be blowing FROM if you’re flying towards a low pressure system?
From the right
Where will the wind be blowing FROM if you’re flying towards a high pressure system?
From the left
What is wind following curved isobars called?
Gradient wind
What is wind following strait isobars called?
Geostrophic winds
What will the pressure and wind direction be if CF is greater than PG?
High and anticlockwise
What will the pressure and wind direction be if PG is greater than CF?
Low and clockwise
At what height will the wind follow the isobars the closest?
About 3000 feet where it is clear of surface friction
Where is the cyclone most destructive?
Forward left quadrant
Which cloud type is associated with heavy continuous rain?
Nimbostratus
In which temperature range is clear ice likely to be most severe?
0 to -15
What are squall lines associated with?
Thunderstorms
When environmental temperature increase with height, said to be what condition?
Stable
Fast moving cold front may be recognised by?
Broken cumulus clouds and rain showers
What happens to IAS and rate of descent with sudden decrease in headwind?
Decrease in IAS
Increase in rate of descent
What is conditional stability?
Saturated air is unstable
Unsaturated air is stable
If you stand with you back to the wind in the southern hemisphere, where will the low pressure be?
Low pressure on right
What are the three conditions for ice to form?
Must be visible moisture
Temperature at or below 0 degrees
Airframe temp must be below 0 degrees
What are the worst icing conditions?
Near freezing level in heavy stratified clouds or in heavy rain
How is rime ice formed?
Small supercooled droplets collide with leading edges have no time to ‘splash’ or spread across skin
What is the temperature range for rime ice?
0 to -40 however it is most common from -10 to -20
What cloud types are you likely to encounter rime ice?
Thin altostratus
altocumulus
Near top of large cumulus
When is clear ice likely to form?
Flying through freezing rain which consist of large droplets.
Large droplets take longer to freeze so they spread
What temperature range is clear ice likely to form?
5 to -15 degrees but most common in 0 to -10
What cloud types is clear ice found in?
Thick altostratus
Thick altocumulus
Just above freezing level of large cumulus, cumulonimbus or nimbostratus
How is hoar frost formed?
Cold soaked aircraft enters layer of warmer humid air, water vapour skips liquid state and goes straight to solid (deposition)
What does frost on the airframe do to surface friction drag, total drag, stall AoA and stall speed?
Surface Friction and Total drag increased
Stall AoA decreased
Stall speed increased
What are the three classifications of icing?
Light (FBL)
Moderate (MOD)
Severe (SEV)
What should you do if you experience light (FBL) icing?
No change of track or altitude is necessary. No speed is lost
What should you do if you experience moderate (MOD) icing?
Change of heading/altitude considered desirable.
Airspeed may be lost
What should you do if you experience severe (SEV) icing?
Change of heading/altitude necessary
Ice builds up and seriously affects performance and manoeuvrability of a/c
What direction is the trade wind in the southern hemisphere?
South easterly
What are the trade wind characteristics?
Blows with consistent velocity Weaker at lower altitudes Generally stable under subsidence inversion of anticyclone Air moist in lower levels Relative humidity high at surface Air is dry above inversion
What season is trade winds responsible for in Australia?
Dry season of north australia
Generally, when does monsoon affect Australia?
Between December and April
What direction winds are there in monsoon?
North westerly
Which direction is the ‘roaring forties’?
Westerly towards sub polar low
What conditions for the roaring forties produce?
Wet windy winters
What is the inter-tropical convergence zone (ITCZ)?
North east or south east trade winds approach each other, causing vigorous convergence in narrow zone
What conditions do the ITCZ produce?
Violent weather
Thunderstorms
Torrential rain
Wind squalls
What conditions are associated with El Nino in eastern Australia?
Drier conditions
What are the conditions for tropical cyclones to form?
Warm tropical oceans about 28 degrees Celsius
Abundant water vapour
Can cyclones form at the equator? Why/why not?
No because Coriolis force is 0 at the equator.
What are the stages of a cyclone?
Formative
Immature
Matture
Decaying
In what stage and where are the strongest winds for a cyclone?
Mature stage
Forward left quadrant
What happens to the pressure gradient in a cyclone as the centre approaches?
Gradually gets steeper
What are cyclones formed from?
Thunderstorms
What are the conditions like in the eye of the cyclone?
Light and variable
Lowest surface pressure
What clouds are associated with cyclones?
Nimbostratus with spiral bound cumulus and cumlionimbus
What latitude do cyclones generally form?
Between 5 and 15 degrees south
What does the surface sea temperature need to be for a cyclone to form?
Approximately 28 degrees
What is the surface pressure around the eye?
Approx 900hPa
What clouds are associated with a cold front?
Cumulus and cumulonimbus
What weather conditions are associated with a cold front?
Thunderstorms, line squalls, severe turbulence and windshear
What will indicate a cold front?
Drop in temperature
Wind backing south west
Cumulus and cumulonimbus clouds
What will indicate a warm front?
Air temperature rise
Dewpoint temperature will be higher
Unstable air
wind backs north west
What is an occluded front?
When a cold front overtakes a warm front
What are subsidence inversions?
Anticyclones of high pressure
Air in top layers sinks with greater adibatic warming than lower layers
What are the cloud levels in aerodrome and trend forecasts?
Above aerodrome level
What are cloud levels for forecasts other than aerodrome and trend forecasts?
Above Mean sea level or flight level
What is an isotherm?
Line on synoptic chart joining equal temperature
The amount of water vapour that air can hold largely depends on what?
Air temperature
What situation is advection fog likely to form?
Warm moist air mass moving over cold surface
What type of clouds are associated with anticyclones?
Stratocumulus and stratus
What are the processes by which moisture is added to unsaturated air?
Heating and condensation
Clouds, fog or dew will always form when?
Water vapour condenses
What are the locations on the pca?
Identifiers used to divide area
What are ‘critical locations’ in ARFOR?
Critical for vfr flight in adverse weather
What does 12/11 on METAR mean?
Temp is 12
Dew point is 11
The equatorial trough moves further north than south because?
Mid summer surface temp are higher at any given latitude in northern hemisphere because of greater land mass
What is the layer of atmosphere in which most of the convection takes place?
Troposphere
The belt of high pressure of Australia during winter is called?
Sub tropical ridge
Monsoon trough features extensive cloud and weather because?
Converging airstream rises over warm ocean due to intensity of solar radiation
There is little convection within the stratosphere because?
Air at top layer is cooler than air at bottom
Pressure gradine force acts in which direction and to/from which system?
At right angle towards low pressure
Surface wind compared to gradient wind backs or veers and faster or slower?
Veers to right and slower
What does surface friction cause in relation to Coriolis force?
Increase CF
Compared to gradient wind, surface wind in Southern Hemisphere is found to be?
Further to right in both highs and lows
For a katabatic wind to form, there must be?
A surface inversion
Strong horizontal wind shear can be found where?
Above strong surface inversion
Light wind beneath radial inversion will cause inversion to become?
Weaker but deeper
Low level jet streams can be hazardous because they produce?
Strong horizontal wind shear near surface
What variations in wind and temperature normally occur with passage of cold front?
Wind backs and temperature falls
Low cloud moving rapidly in warm air ahead of a cold front will likely to produce what?
Squall line
What happens to the central pressure in a tropical cyclone during the mature stage?
Remains constant
A stable layer of air near the height of a ridge will produce what?
Mountain wave activity
There is little vertical development of cloud within the south east trade winds because?
Presence of trade wind inversion
Dust storms are most likely to produce which hazards with regards to visibility and heights?
Severe visibility restriction over wide spread area to heights above 10000feet
What is likely to happen during cumulus (growing) stage of thunderstorm?
Severe airframe icing
