Meterology Flashcards
What are the different layers in the atmosphere?
Troposphere Tropopause Stratosphere Stratopause Mesosphere Mesopause
What gases make up the atmosphere?
Nitrogen - 78%
Oxygen - 21%
Other gases (argon, carbon dioxide, neon, helium etc) - 1%
What happens to the temperature in the troposphere as we gain height?
Temperature decreases
What is the height in the tropopause?
Polar - 25000ft
Tropical - 60000ft
During summer, it is higher
What is the average ISA height in the tropopause?
36090ft
What is the ozone layer and where is it?
Absorber of uv radiation
Irritating, corrosive and colourless gas
In the stratosphere
ISA assumes mean sea level values to be?
Pressure: 1013.25 hPa
Temperature: 15C
Density: 1225 grams cubic meter
At what rate does temperature fall?
2C per 1000ft up to 36090ft
From 36090ft up to 65617ft temp is assumed to be constant at -56C
From 65617 to 104987 ft temp rises at 0.3C/1000ft
Up to about 5000ft, the pressure falls by what?
1hPa per 30ft
In ISA conditions, what will the mean seal level pressure of 1013hPa be at 5000ft?
Approx 845hPa
Why is density important to pilots?
More dense air then the required lift force can be generated at lower true airspeed. Greater engine power is available due to greater mass of each fuel/air charge taken into cylinders.
What happens to pressure as height increases?
Pressure decreases, number of molecules in a cubic metre decreases.
Air becomes less dense, and at 20000ft density is approximately half then at sea level.
What happens to a mass of air as it is heated?
Expands, becoming less dense and rises. Carries it best energy higher into atmosphere. Known as thermal convection
What s advection?
Horizontal motion of air. Brings heat energy and moisture content with it. Aka wind
What is the sea breeze?
Air in contact with earth surface becomes hot by conduction and starts to rise.
Rising air creates isolated area of low pressure over the land setting up a pressure gradient between cool sea and hot land.
Causes cool air from sea to flow towards land
When is the sea breeze greatest?
Mid afternoon on sunny day.
Greater the pressure gradient, greater the sea breeze
What is the land breeze?
Cooling of the earths surface occurs quicker over land than sea.
Cooler air over land blows over the sea having a higher pressure.low pressure gradient
What are katabatic winds?
Unlike other winds which respond to pressure gradient, katabatic responds to force of gravity.
At night, temperature cools down to a point where density becomes greater than that of lower air. Air being more dense means it’s heavier, causing it to descend.
Cool cats come down at night.
What are ideal conditions for katabatic winds?
Strongest at dawn
High plateau slope going down to low terrain
Clear skies over plateau allowing max heat loss at night
Relatively warm surrounding air
What are anabatic winds?
Winds blowing up the terrain
Heating of mountain slope by day causes air mass to become warmer and less dense causing it to flow up the hill.
Generally on westward facing slopes.
Which is generally stronger, katabatic or anabatic winds?
Katabatic due to gravity.
What is fohn wind?
Warmer and drier air on lee side of mountain
What are low level jet streams?
Cause when high pressure system is circulating air anti clockwise along the Australian continent
Freed of surface friction, what speed can low level jet steams get to?
40-50 knots at 2000ft
What are the characteristic of low level jet stream?
Strongest in mornings 06-0900
Can reach 70kts
Usually from the south
Located over a plain, to west of mountain range
May extend from a few 10s to 100s miles in length
Strong lateral and vertical wind shear and turbulence
Normally confined within 3000ft with strong wind about 2000ft
Water exists in how many states in the atmosphere?
Three
Ice
Liquid
Vapour
What two ways can parcel of air reach saturated state?
1-at constant temperature, water vapour can be added until saturation occurs
2-with constant amount of water vapour present, temperature of air can be reduced until no longer hold the vapour
What is relative humidity?
Indicates how close air is to saturation.
Ratio of mass of water vapour actually present in air TO the mass of water vapour which would cause saturation at same temperature and pressure.
=vapour present / vapour possible x 100%
What is dew point temperature?
Temperature at which saturation of given parcel of air occurs
The amount of water vapour that air can hold largely depends on?
Air temperature
Moist stable air flowing upslope can be expected to produce?
Stratiform clouds
Lenticular altocumulus cloud is an indicator of?
Strong turbulence
What conditions are necessary for formation of thunderstorms?
High humidity, lifting force and unstable conditions
What cloud types would indicate convective turbulence?
Towering cumulus
What conditions are fog likely to occur in?
Warm, moist air mass moving over colder land surface
What is the primary difference between rime and clear ice?
Size of water drops/droplets
What is the environmental lapse rate largely determined by?
The stability of the atmosphere
The formation of clouds is largely due to what?
Vertical movement of air and atmospheric stability.
Cloud is formed when parcel of air is cooled to dew point temperature
What is Adiabatic process?
Temperature can change as a result of pressure changes even though best is neither added or subtracted from system.
What is vertical stability?
When a parcel of air rises through the atmosphere it encounters lower pressure and expands.
This expansion causes adiabatic cooling.
What is the dry adiabatic lapse rate? (DALR)
Parcel of unsaturated air rising through atmosphere will cool at 3C per 1000ft
What is the saturated adiabatic lapse rate?
1.5C/1000ft
What does a low environmental lapse rate indicate?
A stable condition
How is stability determined?
From the motion of the air parcels as they rise and descend
What are stable conditions?
Environmental lapse rate very low
Commonly in high pressure systems
Cloud, if any, doesn’t develop until great heights. Stratiform
Precipitation, if any, will be steady
Poor visibility if there are any obscuring particles
Smooth conditions with little or no turbulence
What are the conditions in in stable environment?
Environmental lapse rate will be high Rising warm air will remain warm so will continue to rise Any process which causes a rapid drop in temperature with height will contribute to instability. (Rate at which temp changes with height) Low pressure systems Turbulence Formulation of cumuliform clouds If precipitation, showery rain Good visibility between showers
What are the triggers of cloud formation?
Convection
Orographic uplift
Turbulence and mixing
Widespread ascent (frontal uplifting)
What is convection and what clouds will form as a result of it?
Cold air moving over a warm surface will be warmed from below, becoming less stable.
Tend to rise causing turbulence and good visibility
If moist and unstable, cumuliform clouds will develop as air ascends and cools adiabatically
What is orographic uplift?
Humid air forced to rise over mountain range, it expands and cools as it gains height and rises.
When dew point reached, cloud forms in rising air
What is turbulence mixing?
As air flows over the surface of the earth, frictional effects cause variation in local wind and direction.
What is frontal uplift?
When cold and warm air meet, the heavier cold air remains at the surface forcing the lighter, warm air to rise over it.
Describe cumuliform clouds
When cloud is warmer than the environment
How are cumuliform clouds formed?
Unstable air rising and cooling
What are rain bearing clouds called?
Cumulonimbus
Describe stratiform clouds.
When cloud temperature is equal to or cooler than the environment air.
Generally flat and formed by later of stable air
What are the three cloud classifications?
Low -below 7500
Medium - between 7500 and 20000
High - above 20000ft
What is fog?
Cloud on ground
Visibility below 1000m
Nil turbulence/wind
The structure or type of cloud is determined by?
The stability of air before lifting occurs
Moist stable air flowing upslope can be expected to produce?
Straitform clouds
Why does wind tend to flow parallel to isobars above friction level?
Coriolis force tends to counter balance horizontal pressure gradient
What is the primary difference between rime ice and clear ice?
Size of water drops/droplets
What cloud types are associated with anti cyclone?
Stratocumulus and stratus
What are the processes for adding moisture to unstable air?
Evaporation and sublimination
Unstable, moist air and orographic lifting will most likely produce what?
Cumuliform clouds, good visibility and showery rain
Clouds, fog or dew will always form when?
Water vapour condenses
Cloud height in a METAR refers to height above?
Aerodrome reference point
What periods must TAF for your destination be valid in relation to your ETA?
30min before to at least 60min after
What conditions must be present for formation of thunderstorm?
Atmospheric instability
High humidity
Trigger mechanism
What are the stages of thunderstorms?
Developing (up drafts)
Growing (up drafts)
Mature (up and down drafts)
Dissipating (down drafts)
What are the hazards of thunderstorms?
Severe turbulence
Airframe icing
Lightning
Hail
What is a temperature inversion?
Layer of earths atmosphere in which temperature increases with increase in height
What is a trough?
Elongated ‘finger’ that extends to form low pressure system.
Wind turns sharply to the right
What is a ridge
Elongated finger that extends from area of high pressure.
Wind turns sharply to the left
What is a col?
Area between two highs and two lows
What do closely spaced isobars indicate?
Strong winds
What are the two forces acting upon a parcel of air?
Pressure gradient
Coriolis force
As a general rule, the change in speed and direction over land and sea is?
Land: drops by 2/3 and direction veers by 30 degrees
Sea: drops by 1/3 and direction veers by 10 degrees
