High Altitude Weather Flashcards
What is the life span of a thunderstorm
2 hours
What are the stages of a thunderstorm
Cumulus stage - 5000 to 20000ft
Mature stage - 5000 to 40000ft
Dissipating stage - 5000 to 35000ft
What cloud formation indicates the level of the tropopause?
Anvil.
The tropopause often restricts vertical development of cumulonimbus clouds due to the the temperature inversion which results in a wide spread cloud called Anvil
What is needed for the formation of a thunderstorm to occur?
Source of lift (frontal weather, hot land mass)
Unstable air mass
High moisture content
What are squall lines and how are they depicted on a SIGWX chart?
A sudden, sharp increase in wind speed lasting minutes.
Often associated with frontal air mass and thunderstorms
Can be embedded and closely packed together
Depicted on a chart when thunderstorms are listed as frequent (5/8ths or greater)
Where would you more likely see a thunderstorm exceed the tropopause?
The tropics
Would a thunderstorm caused by a bushfire last shorter or longer than one formed due to a frontal air mass?
Shorter
Thunderstorm up and down drafts can produce rates of climb/descent up to what?
5000ft/minute
both within cell and periphery of the cell (in particular under the anvil)
What cloud formation gives a good indication of which direction the wind is traveling at high altitudes?
Anvil
To avoid the storm ensure to fly upwind rather than down wind.
Where can current information on thunderstorms be found?
Sig Wx Charts
Airmets
Sigmets
Satellite imagery
What are common hazards associated with thunderstorms?
Severe updrafts and downdrafts Line squalls Turbulence Severe icing Heavy rain (tropical storms can hold up to 250mil L of water) Hail Lightning
How do you avoid thunderstorms?
Check all available briefing info during planning
Follow company SOP guidance
Use WX radar and correct operating techniques, do not penetrate any yellow or fly close to sharp colour gradients.
Do not attempt to out-climb a building thunderstorm
Do not attempt to overfly a mature or dissipating storm cell
Avoid active thunderstorms 5nm up to 5000ft or by your altitude divided by 1000 there after
Do not take off or land when a mature or dissipating cell is with 5nm of aerodrome due to microbursts and wind shear
What is Upper Atmospheric Lightening (UAL) and where does it occur?
UAL is lightening arcing between clouds or from the tops of thunderstorms to the bottom of the ionosphere.
Although seldom seen by pilots, it is possible within the tropics, mountainous areas with large orographic uplift or over the ocean where large thunderstorms occur.
What are some types of UAL?
Blue Glimpses Blue Jets Red Sprites Tendrils Halo Elve Giant Jets
Arcing between thunderstorms or out the side of thunderstorms in the arid and sub-tropic regions is not to be considered as UAL.
What are the 2 types of turbulence typically found above FL150?
Clear Air Turbulence or CAT
Mountain Waves
What is CAT and how does it occur?
CAT is sudden and severe turbulence or wind shear occurring in mostly cloudless regions which causes violent buffeting of aircraft.
What cloud formations can be indicators of CAT?
Cirrus or Lenticular clouds
What are the 2 mechanisms that cause CAT?
Mechanical - A disruption to smooth horizontal air flow.
Thermal - Caused by vertical currents of air in an unstable atmosphere
What levels are CAT typically experienced and how are areas of CAT avoided ?
7000ft below the tropopause to 3000ft above the tropopause
Strong vertical and horizontal wind shear associated with CAT tends to be shallow and patchy. A change in 2000ft is usually enough to exit the turbulence.
What are some common causes of CAT?
Jetstreams - significant horizontal wind shear
Terrain - rising ground creates disturbances to air flowing over it
Thunderstorms - CB’s have very strong vertical currents, avoid flying over the top or horizontally by a minimum of 5nm or your Altitude divided by 1000, which ever is greater
Unequal Heating - typically found between the cooler air masses over ocean and the warmer air masses over land.
What does this indicate and what chart would you find it on?
The area inside the line indicates the area that moderate CAT could occur between 8000ft and FL200 on a SIGWX Chart.
A double arrow would indicate sever CAT
How do mountain waves form and where does the turbulence associated with them occur.
Mountain waves are the result of air which is forced to rise up the windward side, then due to atmospheric conditions, sink down the leeward side. This develops into a series of standing waves down stream and may extend 100’s of km over clear areas of land or water and in some cases up through the tropopause.
They need:
windspeed of at least 25kts at/and perpendicular to ridge line.
Windspeed increases with height
A stable layer around the ridge height
How can you visibly identify mountain waves?
Lenticular caps over the ridge line Stacked lenticulars (like venetian blinds) downwind of the ridgeline
What is the name of the turbulent air movement in a mountain wave and how do they occur?
Rotors or eddies can be found embedded in mountain waves.
They normally occur when the windspeed changes due to friction with the ground.
They present as turbulence or wind shear.
Clouds will form on the upwind side of the rotor and dissipate on the down flow side if the air is sufficiently moist
What is a Jetstream and when do they occur?
Relatively narrow bands of strong wind currents >60kts in the upper levels of the atmosphere which blow from West to East
They follow the boundaries between hot and cold air masses
Which side of a jet stream is the wind shear greatest?
It is usually greatest on the cold side of the jet stream
If there is CAT in the area it is stronger on the cold side, next to and under the axis of the Jet
What time of year are jet streams stronger?
Stronger during the winter months when the hot cold boundaries are more pronounced
What direction do jet streams flow and why?
West to East
Due to the rotation of the earth
What are the two jet streams called and what direction do they move throughout the seasons?
Polar Jetstream - FL230 to FL390 (between the Polar and Ferrel circulation cells)
Sub-tropical jet stream - FL330 to FL520 (between the Ferrel and Hadley circulation cells)
The sub tropical jet moves poleward in summer and towards the equator in winter.
How is the jet streams speed created?
Warm air in the Hadley cell rises at the equator then gets pushed towards the poles where it meets the Ferrel cell. Due to the earths rotational speed the air above the earth has momentum proportional to the speed of rotation directly below. As air moves from the equator towards the poles its momentum remains the same but the earth below it slows creating the jet stream speed.
What factors effect the speed, level and latitude of a jet stream?
Location of high and low pressure systems
Warm and cold air masses
Jet streams have a tendency to move with the sun so as elevation changes during the seasons, so do the jet streams
What is the core speed of this jet stream symbol?
50 + 10 + 10 + 5 = 75kts
Why is volcanic ash so bad for aircraft?
It is very abrasive to forward facing surfaces including windscreens, fuselage surfaces, compressor fan blades etc.
Inside the engine it can be melted by the engine, where it can then re-solidify after being deposited on cooler parts degrading overall engine performance
What are signs of an encounter with volcanic ash?
Odor - can smell like electrical smoke, burnt dust or sulfur
Haze - within the cabin that can settle on surfaces
Engine conditions - surging, torching from tailpipe, flameouts, temperature changes, white glow at inlet
Airspeed - airspeed can fluctuate erratically if blocked
Pressurisation - cabin pressure can change including loss of pressurisation
Static discharges - similar to St. Elmo’s Fire, a glow and blue coloured sparks on windshield
Radio - Garble radio transmissions
Navigation - can interfere with electronic systems
There are 4 ‘alert level’ colours to indicate volcano activity and associated volcanic ash. What do they mean?
What indicates the level of the tropopause on a high level SIGWX chart?
Box with the level
Pentagon signifies areas of high or low levels of the tropopause
What high altitude charts should be briefed prior to flight and why?
SIGWX - their associated symbology will give an indication on areas of poor weather to avoid i.e. CAT or areas you can fly to increase performance i.e. a flight east within a jet stream
Wind and Temp Charts - can indicate areas of the tropopause
GPWT - wind speed/direction and temp for last minute diversions/change in levels
RSWT - ensuring best level has been selected for flight
