intro_to_aviation_block_4_20180401181938 Flashcards
how many thunderstorms are there at any given moment around the world
12 000
what are the only clouds that produce thunderstorms
CB, Cumulonimbus
what are the three requirements for thunderstorm formation
- unstable air (especially is unstable to high levels)2. Some from of lifting action to get the air moving upward3. air with high moisture content
What are the three stages of a thunderstorm
- the cumulus stage2. The mature stage3. The Dissipating Stage
Explain the cumulus stage
this stage is characterized by the formation of a cumulus cloud, that builds up to a towering cumulus, the cloud has mostly updrafts which support the water droplets within the cloud and no precipitation occurs
explain the mature stage
is characterized by the build up into TCU/CB with very high tops. The updrafts within the cloud may attain 6000 feet/min. as the water droplets grow they start falling and drag air down with them, producing down drafts in the 2000ft/min range. this is the stage where most if not all the precipitation occurs. There is violent turbulence associated with the updrafts and downdrafts. Lighting, micro bursts, gust fronts, hail, tornadoes, and heavy precipitation are all associated with the mature stage
The Dissipating stage
the onset of precipitation is the key to the dissipation of the thunderstorm cell. The precipitation cools down the lower part of the cloud, and breaks the updrafts that are the main source of its energy. The top of the cloud spreads out into anvil form.
What are the two main types of thunderstorms
- air mass thunderstorms- frontal thunderstorms
explain airmass thunderstorms
usually Form as a result of convection or orographic lift. Form individually or in clusters. Large clusters are collectively known as supercell
Frontal thunderstorms
Are mostly associated with cold fronts but also occur with warm fronts. They usually form in a solid line several hundred miles long and in various stages of development. Warm front thunderstorms are often embedded in the main cloud deck and not as visible as cold front thunderstorms.
What is an convection thunderstorm
scattered cloud, unequal heating of the ground,
Advection Thunderstorms
Advection of cold air over a warm surface
Orographic Thunderstorms,
air is lifted by sloping ground
What are the three concepts related to air movement
- Gust fronts- Downburst- Downdrafts speed
Explain Gust front as related to thunderstorm activity:
- strong downdrafts at mature stage- downdrafts spread out when reach ground- significant turbulence
what are the two kinds of down bursts
Micro bursts and macro bursts
Explain micro bursts
is a downburst of less then 2 miles in diameter and of short duration, typically less then 5 mins, can be wet or dry depending on precipitation
Explain macro bursts
a large downburst with a diameter of 2 miles or more when it reaches the earths surface, damaging winds can last from 5 to 20 mins
What does a downdraft in micro bursts do
vertical speed approaching 6000 feet/min as they reach the ground the spread out giving horizantal wind as much as 80 knots. Multiple micro bursts are common.
What is virga
precipitation falling but not reaching the ground, associated with TCU and CB are ofter precursors of microbursts. The virgo evaporates below the cloud and as a result of the heat required for evaporation, the air in these regions become colder than its environment, sinking rapidly and accelerating downwards.
Micro burst read over
Downward vertical winds can attain speeds as high as 6 000 feet/min (110 km/h). Outward horizontal wind guest speeds can reach up to 80 knots 140 kph at tree top levels The micro burst downdraft shaft can have a diameter of up to 6 000 feet 1.8 kmat ground level the vortex ring can have a horizontal extent of up to 2 1/2 mile (4 km) from the centre of the microburst.Microbursts do not have a long life span, lasting typically about 10 to 20 minutes, with the maximum wind intesities occurring about 5 mins after ground contact and lasting for about 2 mins.
What are the nine areas of concern when flying near a thunderstore
- Turbulence2. hail3. lightning4. icing5. squall lines6. tornadoes7. low ceilings and visibilities8. heavy rain showers9. microbursts
Turbulence
- strongest in a cumulonimbus cloud near the shear zone between the updrafts and down drafts (between 12000 and 20000 feet in the mature stage)- outside the cloud LLWS is presents below the cloud and is caused by downdrafts that race towards the ground Turbulence is also possible above the cloud (up to several thousands of metres) and outward up to 30 km. Often a roll cloud on the leading edge of the storm marks the position of the eddies in this shear zone, and is most prevalent with cold fronts and squall lines.
Hail
- occurs in the mature stage of cells that have updrafts of more then usual intensity. - Around 10 000 to 15 000 feet- if the cloud is built up diagonally, hail that has been carried aloft in the updraft may be cast out into the clear air surrounding the cloud, from the sides or from the overhanging anvil cloud
Lightning
- he visible electric discharge produced by a thunderstorm. - It occurs in cloud (also called sheet lightning), cloud to cloud, cloud to ground and occasionally cloud to clear air- is always present or in the vicinity of cumulonimbus clouds- most present in CB clouds between 8 and -8 degrees celsius in the mature stage.- this is rarely a major hazard to aircraft but can cause the folowing: - Puncture the skin of the aircraft. - Damage communication and navigational equipment. - Temporally blind pilots. - Induce errors in magnetic compasses. - Disrupt low and medium radio frequencies. - More rarely, ignite fuel vapours.
Icing
- The most dangerous icing can occur in thunderstorms - clear and mixed icing is possible in all stages of development of thunderstorm clouds but severe clear icing is most likely in the upper half of thunderstorm cloud in the mature stage, especially when the temperatures are between 0 and -25 C- remember that strong up and downdrafts can rise or lower the freezing level within a thunderstorm cloud. It should also be remembered that a cluster of thunderstorm clounds could include several cells at various stages of development.
Squall Lines;
- a on frontal narrow band of highly active thunderstorms- can generally develop ahead a cold front in moist an unstable ai. It can for rapidly, reaching maximum intensity during the late afternoon r early evening hours. They can range from one to several hundred miles in length, and can be broken or in a continuous line.- A squall line can contain extremely sever thunderstorms (Torrential rains, large hail and tornadoes) and have all the other hazards generally associated with thunderstorms.
Tornadoes
- occur with isolated thunderstorms at times, but occur much more frequently with superecllular thunderstorms associated with cold fronts and squall lines- since vortex extends well up into the cloud a hidden vortex could be countered without seeing it- tornadoes can occur several kilometres outward from the main area of lightning and precipitation. cumulonimbus mamma cloud (round shaped under hanging below he cloud base or anvil) is often a signpost to tornadoes and violent turbulence
Low ceilings and visibilities:
- The visibility is generally near zero within a thunderstorm cloud. The ceiling and visibility aslo can greatly become reduces in the precipitation between he cloud base ad the ground. Heavy precipitation can saturate the ar rapidly causing stratus fractious and for to form rapidly reducing ceilings and visibility turning VFR approach into an IFR approach.- air craft would be restricted in these conditions, but the hazards become manifold when accompanies by other hazards such as turbulence, hail, lightning and low level wind shear, making precision instrument flying very difficult.
Heavy Rain Showers;
- the heaviest rain showers are associated with the mature stage of development with the onset of the first downdrafts- heavy rain showers associated with thunderstorms can cause contamination of the wing surface which results in early stall. If encountered during approach and landing, heavy rain can reduce visibility and cause refraction on the windscreen of the aircraft, procing an illusion that the runway threshold is lower than it actually is.- Water lying on the runway cause hydroplaning which destroys the braking action of the aircraft. Hydroplanning can also lead to loss of control during take-off
Micro Bursts;
- main effect is to cause sudden and dangerous low level wind shear, causing hazardous conditions for take-off and landing.
how cold can supercooled water droplets stay liquid to
-40C
What droplets freeze at warmer temperatures, bigger or smaller
larger
what kinda cloud makes the most frequent icing conditions
Stratocumulus
what cloud makes the heaviest icing potential
Cumulus, Towering cumulus and cumulonimbus
The amount of icing is directly related to…
the size of the water droplets
The size of the droplets is directly related to…
the vertical velocities within a cloud