Revision Deck Flashcards
1
Q
Define Air frame Icing
A
Icing that accumulates on the outside of the aircraft both during flight and on the ground.
2
Q
What are the types of airframe icing (6)
A
- Rime ice
- Clear (glaze) ice
- Mixed ice
- Hoar frost
(5. Freezing drizzle - Freezing Rain)
3
Q
What are the two forms of aerosols
A
- Condensation nuclei (very common)
- Freezing nuclei (only a small number of these - required for a SCWD to freeze)
4
Q
What are super cooled water droplets
A
SCWD are water droplets that have reached zero degrees but do not have a suitable freezing nuclei, so they remain liquid below zero.
5
Q
Characteristics of Rime ice. Any consequences?
SCWDs
TEMPS
APPEARANCE
DANGERS
A
- Forms at higher altitudes
- Colder temperatures (-20 to -40 degrees)
- Bright white appearance and brittle (due to air being trapped during rapid freezing process)
- Not heavy
- If left to build up over a long period of time it can begin to affect control/lift of a/c. Easy to get rid of via manoeuvering
6
Q
Characteristics of Clear (glaze) ice. Any consequences?
SCWDs
TEMPS (3)
APPEARANCE
DANGERS
A
- Most severe form of icing.
- Found in clouds with high liquid water content and warmer temps (zero to -20 degrees). most severe between -5 to -8 degrees. (most common -15 to -25)
- SCWDs are large and numerous.
- Clear, sheet - like appearance. Hard to see, heavy.
- If left too long, ridges and horns can develop on top and below the wing (at 45 degree angles). Profound effect on lift and can cause uncommanded deflection and accidents. Extremely hard to get rid of
7
Q
Formation of clear (glaze) ice
A
- Because the SCWDs are large and numerous, freezing process is not instantaneous.
- Portion of droplet will freeze on contact, latent heat released slows the freezing process, allowing droplet to spread back across the wing before freezing.
- droplets join, air bubbles are expelled, strong adherence to SFC of wing.
8
Q
Characteristics of Mixed ice
SCWDs (what clouds?)
TEMPS
APPEARANCE
DANGERS
A
- Combination of a range of SCWDs sizes. (suggests both cumuliform and stratiform clouds)
- Rime ice visible on leading edges.
- Clear/glaze ice not visible on the rest of the wing.
- Occurs between -10 to -25 degrees (most likely between -10 to -15).
- General rule: treat all mixed ice as a case of clear ice.
9
Q
Characteristics of Hoar Frost.
Can it occur during flight?
A
- Forms when moist air/water vapour comes in contact with a sub-zero a/c surface. (DEPOSITION).
- Can cover entire air frame and dangerous to take off without getting rid of it (disrupts lift = stall).
- Generally occurs on the ground but can occur during flight in clear air above the FZL, whe the a/c is cooled to sub-zero temps and then flies into high humidity.
10
Q
Cloud types associated with Rime ice
A
- If the FZL is very low: Stratocumulus and stratus
- Altostratus and Altocumulus
11
Q
Cloud types associated with clear ice
A
- Cb, Tcu, Nimbostratus, altocumulus lenticularis clouds (updrafting portion in special conditions).
12
Q
General height ranges relative to FZL (rime/clear/mixed)
A
- Clear: 1500 - 6000ft above FZL (commonly) or updrafting section of lenticularis_
- Mixed: 5000 - 12500 above FZL (commonly)
- Rime: 7500 - 15000ft above FZL
13
Q
Hazards of air frame icing in flight (aeros based) (3)
A
- Changes in the 4 forces acting on the a/c in flight (D and W increase, L and T decrease)
- Tail Plane stalling (generally before the main plane)
- Main plane stalling
14
Q
Hazards of air frame icing (Structure based damage) (5)
A
- Damage to surfaces from chunks of ice breaking off forward surfaces.
- Damage to engines from ice ingestion.
- Uneven ice distribution resulting in severe vibration and structural failiure.
- Poor radio comms due to ice build up on antennas.
- Poor visibility due ice on windshield.
15
Q
Hazards of air frame icing (Performance based) (6)
A
- Intake icing (reduces intake of air into engine, less power generated).
- Pitot tubes/static vents icing over.
- Propeller icing (can alter shape of blades = less thrust.)
- Landing gear doors frozen shut
- Control surfaces freezing solid
- Uncommanded full deflection of control surfaces
16
Q
Conditions required for Cb development
A
- An adequate amount of water vapour at low levels
- Conditional instability through depth in the atmosphere (= release of latent heat)
- Trigger mechanism to initiate lifting
17
Q
Types of trigger mechanisms for TS development
A
- Convection (parcels of air gaining buoyancy through contact with a warm SFC)
- Orography (ascent via contact with mountains etc)
- Frontal lifting (widespread ascent)
18
Q
Classifications of Thunderstorms
A
- Airmass (parcel of air with similar characteristics)
- Frontal (boundary b/t two different types of airmasses, triggered by 3 main mechanisms)
19
Q
The lifecycle of a TS
A
- Cumulus stage
- Mature stage
- Anvil/dissipating stage
Overall time of life cycle is 1.5 hrs.
20
Q
Describe the cumulus stage in the life cycle of a TS
Any dangers at this stage? Time taken?
A
- Trigger initiates lifting, a TCU begins to form. (lots of latent heat released)
- There are only updrafting winds in a TCU, which carries SCWDs upwards.
- Some SCWDs freeze, creating snow and ice. Eventually enough of these form at the top for it to fall, melt and create the first rain at the SFC.
- Nil dangers except possible severe icing at this stage (dude large qty of SCWDs lifting, turb only light - moderate (no downdrafts to worry about). 30 mins.
21
Q
Describe the mature stage in the life cycle of a TS
Any dangers? Time Taken?
A
- First heavy rain at SFC
- An anvil will begin to form at the top of the cloud as the SCWDs begin to spread out horizontally beneath the tropopause.
- Any of the EIGHT hazards now exist, tornadoes are unlikely however from stationary Cbs. 30 mins.
22
Q
Describe the Anvil/Dissipating stage of a TS
Any dangers? Time taken?
A
- The top of the anvil will start to become fibrous (due to formation of cirrus)
- Updrafts cease and hazards start to dissipate. 30 mins.
23
Q
List the hazards created by Cb (8)
A
- Severe turbulence (due up/down drafts - centre to base should be avoided)
- Severe icing (in clusters of Cb, area above FZL 0 to -12 degrees should be avoided)
- Electrical phenomena (Lightning/static charges)
- Hail (ice crystals cycled in up/down drafts)
- Poor Visibility (due heavy precip)
- Tornadoes (in severe TS, over water they are called waterspouts, both are rare in NZ)
- Microbursts
- First gust/gust front. (sudden strong downdraft of cold, dense air = Low level wind shear, characterised by roll clouds)
24
Q
Define Microbursts
Characterised by?
Intensity and lifespan?
2 Types
A
- Localised severe wind pattern driven by extremely strong downdrafts from dense, cooled air. Can exceed 100kts in the vertical.
- Microburst winds intensify 5 mins after touch down, general lifespan is 15 mins.
- Can be Dry (occur with high based TS, rain evaporates before reaching SFC. More dangerous)
- Can be Wet (When precip accompanies microburst to SFC. More common in NZ due moist lower atmosphere)
25
Development of Hailstones
- Only occur within Cb clouds with up/down drafting air.
- Number of times the ice crystal cycles up and down the Cb before it gets too heavy and falls out defines size and number of layers of:
Rime ice (upper Cb)
Clear ice (lower Cb)
- Hail can fall out of: Anvil/sides/bottom of Cb.
26
How to avoid TS
1. Avoid in planning phase! (use radar in flight)
2. have an alternate route
3. Don't fly under orographic TS (downdrafts)
4. Cross frontal TS at right angles
27
What influences the flow of wind (5)
1. Wind strength
2. Angle of wind flow near the ranges
3. Shape of the mountain range
4. Stability of the air
5. Vertical profile of wind speed and direction
28
Requirements favourable for lee wave development (5)
1. Min 20kts at ridge top level
2. Increasing wind speed with height (creates overturning motion)
3. Wind perpendicular to ridge line (or within 30 degrees to perpendicular)
4. Wind direction not varying with height
5. Stable layer at about ridge top level.
29
Define the formation of Rotor streaming
Occurs when strong winds blow across a ridge line (Easterlies), with a marked decrease in speed above ridge level (Westerlies). Lee waves will not form. However, a single rotor will format ridge top, lee of the range and can migrate further lee of the range.
30
Conditions required for rotor streaming
1. Winds near perpendicular to ridge line
2. Strong winds at ridge top height, but decreasing above.
31
Features of rotor streaming
1. Severe turb in rotor zone on the lee side and in line with or just below of the ridge line.
2. Relatively smooth airflow above ridge top level.
32
Define the Fohn wind
Where does it occur often in NZ?
A warm, dry, very gusty wind blowing down the lee side of a major mountain range.
The Strong NW that blows across the canterbury plains to CHCH is a Fohn wind.
33
How is a Fohn wind formed
How is this related to the lapse rate.
1. Air rises on windward side of a range
2. Cloud forms, releasing latent heat (from condensation)
3. Rainfall will occur on the windward side, reducing water vapour in the air.
4. wind on lee side is therefore hot, dry and strong
Windward side: DALR (-3 deg per 1000ft) and SALR (-1.5 deg per 1000ft)
Top of range down lee side: - DALR (-3 deg per 1000ft)
34
Features of a Fohn wind
- Fohn gap (band of clear skies in lee of the ranges due descending air)
- High cloud bases on lee side
- Turbulent conditions
- Lee wave activity
- Warm temperatures to the east of the country
35
Dangers of flying in Lee Wave conditions
1. Strong downdrafts
2. Rising ground
3. Low ground speed
4. Risk of rotors with sever turb.
36
Features of lee waves (7)
1. Bands of lifting and sinking air parallel to range
2. AC Lenticularis and rotors present (visible w sufficient moisture)
3. Severe turb in rotor zones
4. High level clear air turb if jet stream is present
5. Smooth flying in wave system above friction layer (downdrafts can exceed climb performance of a/c)
6. Downdrafts can touchdown to SFC = localised strong winds
7. Severe icing in updrafting portion of wave clouds under special circumstances.
37
Describe Lee Wave formation
1. Air displaced upwards over the Range hits a stable layer at ridge - height, this provides restoring force for the descent of the air on the leeward side.
2. A pendulum effect is formed downstream
38
What are the components of air flow?
1. Translation
2. Rotation (clockwise or anticlockwise)
3. Divergence (and) Convergence
4. Deformation
39
Define translation
The movement of a parcel of air from A to B (in any direction) without rotating/altering its shape or volume.
40
Define Divergence
Occurs when a body of air expands horizontally. More precisely, a fixed volume of air is divergent when horizontal outflow EXCEEDS the horizontal inflow.
41
Define convergence
Occurs when a body of air contracts horizontally. More precisely, a fixed volume of air is convergent when horizontal inflow EXCEEDS the horizontal outflow.
42
Define confluence and diffluence and describe how they work relative to conversion/diversion
Confluence: Wind streamlines coming together
Diffluence: Wind streamlines moving apart.
-Both can influence conversion/diversion generated, however, Confluence/Diffluence can exist without conversion/diversion.
43
Generic rules for Divergence and Convergence (3)
1. The net inflow must equal the net outflow.
2. Divergence and convergence only work within the horizontal.
3. The horizontal deficit/excess is made up for by vertical inflow (DIV) or outflow (CON)
44
Describe how conversion works in a parcel of air
1. Inflow of 20kts in horizontal
2. Outflow of 10kts in the horizontal
3. Therefore a loss of 10kts vertically.
- Loss of 10kts in the vertical induces low pressure system at the SFC. Tropopause will sink.
45
Describe how diversion works in a parcel of air
1. Inflow of 10kts in horizontal
2. Outflow of 20kts in horizontal
3. Therefore a gain of 10kts vertically
- Gain of 10kts in the vertical induces high pressure system at the SFC. Tropopause will rise
46
Why are conversion and diversion important?
What causes them?
Because they lead to vertical motions in the atmosphere, which in turn results in cloud and precip formation, as well as cloud suppression.
Changes in absolute vorticity
47
How does pressure in a Low/high system increase or decrease due to DIV and CONV?
- Increase in CONV at the SFC = increase in ASCENT of air, therefore results in an increase in the low pressure system at the SFC (and vice versa)
- Increase in DIV at the SFC = Increase in DESCENT of air, therefore results in an increase of high pressure system at the SFC (as more air gets stacked on top of the point - subsidence)
- At the top of the troposphere, CONV leads to descent, and DIV leads to ascent.
48
Define curvature vorticity
Occurs in the bends of both anticyclones and cyclones and rotates in the direction of the wind around the pressure system.
49
Define Shear vorticity
Occurs in straight isobars around both Low and High pressure systems, and occurs due to the difference in faster and slower moving air. (like a barrier jet).
50
Define relative vorticity
The sum of the curvature and shear vorticities gives the relative vorticity. Which is relative to the SFC of the earth and can be cyclonic or anticyclonic in nature.
51
Define the Earths vorticity
Arises from the shear produced by the earths rotation around its axis, and increases in strength with latitude (towards the poles).
52
Define Absolute vorticity
(3) points about absolute vorticity
Is the sum of relative vorticity plus the earths vorticity.
1. Earths vorticity is much greater than Relative vorticity.
2. Earths vorticity is always cyclonic (in Southern Hemisphere)
3. Therefore Absolute vorticity is ALWAYS cyclonic in nature.
53
What does change in Absolute vorticity cause?
1. Conversion/diversion are affected
2. Ascent or subsidence of the columns of air above these systems are affected (High/Low pressure systems)
3. Therefore the development or decay of cloud/precip is affected.
54
General rule for Absolute vorticity relative to CONV and DIV
1. Increase in AV = Convergence (Low pressure at SFC)
2. Decrease in AV = Divergence (High pressure at SFC)
55
Define Deformation
Occurs when a body of air changes its shape. When it happens, both confluence and diffluence are present. (think of CT4 diagrams)
56
Define Anticyclone (high)
A region of relatively high pressure, with winds circulating around the point with the highest pressure anticlockwise in the Southern Hemisphere.
57
Features of an Anticyclone (5)
1. Divergence at the SFC
2. Air subsides from above (creating high pressure at SFC)
3. Anticlockwise winds in SH
4. Surrounded by at least one more or less circular isobar.
5. associated with light winds and warm temps
58
Give an example of a warm anticyclone
Discuss how they are formed
- Sub tropical highs
1. General circulation causes air to rise at equator
2. This moves South in the high troposphere, cooling and converging - this causes the air to sink to the SFC (convergence occurs faster than outflow @ SFC)
3. As dry air from aloft sinks, it warms at DALR = warm
4. This results in high pressure system created at SFC (generally around 30deg South).
59
How are warm anticyclones intensified
- Increased absolute vorticity above developing high (creates more convergence within jetstream over the high, downward motion is enhanced = intensified high).
60
Type/height of inversion found in warm anticyclones
Usually a Subsidence (temp) inversion b/t 3000 - 8000ft
61
Discuss the formation of a cold anticyclone
Give an example overseas and in NZ of where these can form
1. Air in contact with SFC cools via conduction and becomes more dense.
2. SFC pressure increases as a result, the anticyclone is formed. (super shallow systems - only about 3 to 5000ft)
E.g. (usually develop in winter)
- Siberian High
- Occur in inland parts of NZ in winter e.g. Central Otago
62
What are the (7) hazards associated with Anticyclones
1. Convective Showers (on exposed coast to E of high)
2. Extensive low cloud (100 - 500ft)
3. Poor Vis due to Drizzle on W of High
4. High winds and turb on fringes of High
5. Haze due to trapped aerosols beneath inversions
6. Fog due to radiation cooling under clear skies in centre of High.
7. Summertime TS due increasing divergence aloft and not enough SFC heating to overcome subsidence inversion. Sea breezes can assist
63
Define a Front
The boundary between two airmasses with differing characteristics (temp/pressure).
64
Define an air mass
A large body of air whose physical characteristics, particularly temp and humidity, are approximately the same over large horizontal distances (100s of KMs)
65
What are the four Air mass source regions
And what does air mass source region define
(A): Antarctic (Very cold)
(P): Polar (Cold)
(T): Tropical (Warm)
(E): Equatorial (Warmer/hot)
Defines the temperature properties of the airmass
66
What else defines and is assigned to air masses?
Whether the air is moist or dry:
(m): Maritime (Moist)
(c): Continental (Dry)
67
What are the only two Air masses experienced in NZ
mT (Maritime tropical)
mP (Maritime Polar)
68
Summary of a Southerly (mP) flow onto NZ
- Cold, moist mP air moving north from the S or SW, heated from the SFC
- Air mass becomes increasingly unstable
- Air begins to rise (convection) and cool adiabatically, forming Cb/Tcu/Cu.
- Results in SH of rain, hail, snow and sleet.
- Poor vis at times and often turbulent
69
Summary of a Northerly (mT) flow onto NZ
- Warm, moist mT air moving South from the North, Cooled from the SFC
- An inversion and increased stability are created
- Due to the cooling, any lifting results in stratiform cloud (St, Sc, As, Cs), with low bases possible, fog can form.
- Continuous Rain or drizzle and poor vis, with light - moderate turbulence.
70
What are active fronts characterised by? (4)
1. Large temp gradient across the front
2. Moving at >30kts across SFC
3. Front located under an area of upper level divergence
4. Polar frontal jetstream associated with the front has a strong N to S component to its flow
71
What are the characteristics of a cold front (6)
1. Rapid movement (15 -40kts)
2. Marked temp drop as front goes through
3. Abrupt wind change from Northerly 1/4 to SW 1/4 in Southern Hemisphere
4. Sharp pressure rise in the colder, heavier air mass following the front.
5. Cumuliform clouds with SH of rain, hail or snow
6. Narrow band of precip, usually just prior to wind change.
72
Define a depression
A closed off area of relatively low atmospheric pressure. Also called a 'low' or 'cyclone'.
73
General characteristics of Depressions (relative to CONV and DIV)
1. Convergence at low levels (due to friction near SFC, causing wind to blow slightly across the isobars towards lower pressure)
2. Divergence at upper levels due air moving through an area of decreasing absolute vorticity.
3. Upward motion due low level CONV and upper level DIV.
4. Thick cloud formation/precip due upward motion (concentrated around the front)
74
How does the upper air pattern work to lower or intensify Depressions at the SFC
1. DIV aloft results in vertical motion
2. If upward motion generated at the top of the troposphere exceeds upward motion generated by frictional CONV at the SFC more air is removed from air at top of column that is entering it at the bottom.
3. Pressure at SFC falls and low will develop.
- Enhanced/deepened when there is a considerable amount more DIV aloft than CONV at SFC.
75
Factors (4) intensifying the upward motion of air.
1. Sharpness of the curvature around the upper trough/ridge. (increase in sharpness = increase in vorticity and vice versa)
2. An increase in shear vorticity (from passage of jet stream over area)
3. Increased diffluence (spreading out of isobars downstream of upper trough)
4. Cloud development (releases latent heat, destablises air which accelerates up drafting air).
76
Important aspects of Lee Depressions for aviation (3)
1. Usually associated with strong winds = mechanical turb and lee wave activity in lee of ranges.
2. Significant cloud and vis problems due precip on windward side. On lee side, there should be nil cloud/precip.
3. Combined effects of windward ridge and Lee trough can result in large QNH changes over short distances
77
Important aspects of Thermal Lows for aviation (3)
1. Convective turbulence as a result of thermals
2. Possible afternoon Cbs with showers, TS and hail
3. Warm temps and low pressures increases the density ALT and decreases take-off performance.
78
What is a thermal or heat Low
A shallow Low pressure system caused by the heating of the SFC and air near it.
1. Air near SFC is heated, becomes less dense and bouyant.
2. Convection (rising) occurs.
3. Divergence between 2 - 5000ft occurs, SFC pressure is lowered and Low pressure system created.
79
What is a Lee depression/how does it occur?
Is formed in strong wind conditions in the Lee of a range or mountain, (doesn't behave the same as a normal low pressure system. Occurs when;
- An airmass is forced over/around a mountain barrier
- Build up of air on windward side = high pressure
- Corresponding drop in pressure on Lee side
80
What is the cause for Convergence at the SFC
Surface Friction which results in the wind blowing slightly across the isobars.
81
What are the 2 formation processes for depressions
Which of these is likely to produce TS
What enhances this process?
- Warm and Cold formation processes.
- Cold formation process is most likely to produce TS (upper trough approaches area of Cu or Cb = upper level DIV which results in ascent and increase in convection cloud generation)
- Further enhanced if a jet stream is also present.
82
Common problems with WX radar? (7)
1. Attenuation (weakening of radar beam by curtain of heavy precip, rainfall beyond curtain look minimal when it actually isn't)
2. Ground echoes/Ducting (bouncing b/t terrain and strong inversions)
3. Sea clutter (due side lobes picking up sea waves)
4. Radar elevation (Further the distance from the radar, the higher the beam, only high level precip picked up)
5. False echoes at sunrise/sunset (Due radar picking up sun radiation - seen as a straight line on image)
6. Bugs on radar (looks like virga)
7. Other interference lines (Due someone illegally transmitting on the same frequency as the radar - Looks like a long line from single pt.)
83
Rule for radar and satellites
- Radar from below
- Satellites from above
84
Disadvantages of Polar orbiting satellites (2)
1. At lower ALTs it takes 12hrs for the satellite to appear overhead again. (NZ gets images from 2 satellites = 4 passes each day)
2. Cannot provide continuous view of one location
85
Disadvantages for Geostationary satellites (3)
1. Distortion at higher latitudes due to angle of viewing
2. Lower resolution
3. Costlier to deploy
86
Features of Polar orbiting satellites (ALT, FoV, Res, Passes/frequency, WX functions)
- ALT: 850km above SFC of the earth. (3000km field of view)
- Low level , high resolution. (375 - 705m per pixel)
- Passes over poles every 105mins (changing angle results in complete coverage of earths SFC every 12hrs.
- WX functions: IR/VIS imagery, Sea SFC temp, vertical temp and moisture profiles
87
Features of geostationary satellites (ALT, FoV, Res, Passes/frequency, WX functions)
- ALT: 36,000km above SFC of the earth. (Field of view is full hemisphere)
- High level, low res (1-2km per pixel)
- Five positioned around the globe (we use Himuwari)
- Images provided every 10-15 mins 24/7
- WX functions: IR/VIS imagery, Sea SFC temps, collection/transmission of data from floating buoys and remote AWS, Tracking of CLD and water vapour (provides upper winds)
88
What is a thermal wind?
What is another name for a thermal wind?
The differences between winds at differing levels (shears) due to temperature differences (temp gradient), also known as the 'vertical geostrophic wind shear'.
89
What components are required to calculate upper level winds (and what is the trick?)
1. SFC wind direction and speed
2. Thermal wind direction and Speed.
Both these can be used to calculate the upper SFC wind speed and direction.
SFC + Thermal = Upper
90
What Thermal wind does the southern hemisphere experience?
Generally, the temperature gradient that drives the SH thermal wind slopes from the equator (warm) to the Poles (cold). However, due to Coriolis Force, the wind bends to form a westerly thermal wind.
91
Define a Jet Stream
A region of strong winds, sustaining 60kts or more.
92
What are the characteristics of the Polar front jet (PFJ) (6)
1. Driven by large temp differences found above frontal zones (thermal wind)
2. Located near 50 - 60 deg Latitude zone, North of cold polar air masses
3. Not continuous around the globe (due frontal)
4. Often have large Northerly/Southerly component, always a westerly component.
5. found at 30,000ft in warm air, a few deg poleward of SFC front.
6. Wind Max in NZ area 80-100kts, can reach 200kts
93
What are the characteristics of the Sub-tropical jet (STJ) (5)
1. Driven by conservation of angular momentum as fast moving air from equator descends on mid-latitudes
2. Located above sub-tropical belt of high pressure (25 - 35deg)
3. Very zonal, only a few deg N or S of Westerly
4. Found at 40,000ft
5. Wind Max in NZ 80kts in summer, 120kts in winter, can reach 200kts.
94
Cloud characteristics (associated with jetstreams)
Cirrus on equatorial side, and clear skies on poleward side.
95
Cause of CAT
Dynamic instability
96
Restrictions on flight around Ruapehu
Is currently at alert level 1, due to this, flight must be:
- 3nm from the vent
- Upper limit is 12,200ft AMSL
It is a recommendation to fly outside of this bubble, it is not a ban. (Hazard area)
97
Avoidance and alleviation from volcanic activity
1. Avoid in planning stage if possible
2. If ash is encountered in flight:
- Engines to idle if possible + autothrottles off
- Exit ash cloud immediately (180 deg descending turn is the quickest exit strategy).
- Turn on engine and wing anti - ice devices
98
What are the 12 hazards of volcanoes?
1. Jet engine flameout (Due tiny glass particles in the air)
2. Fan blade erosion and build up of ash in engine
3. Blockage of pitot tubes
4. Poor or nil radio reception
5. Vis through windshield can be reduced to nothing (due pitting by glass particle)
6. Contamination of engine oil
7. Loss of cabin pressure
8. St Elmos fire (blue electrical tendrils - occur in Cb also)
9. Light dust can enter the cabin, looks like smoke, as well as an acrid smell which smells like electrical smoke
10. Wet volcanic ash can make the RWY slippery
11. paint can be stripped from a/c
12. Dry ash on ground can also be sucked into engines.
99
What is the threshold windspeed for blizzard to occur?
What does it depend on?
- Depends on temperatures/stability of atmosphere and size/shape of snow particles (therefore, the age and how dry the snow cover is)
- New snow: 10kts
- Old snow: up to 40kts required
100
Define Whiteout
An optical phenomenon that occurs due to diffuse illumination (Light that comes from all directions and scatters with equal intensity as opposed to direct light.) in uniformly overcast conditions over snow covered SFCs.
101
Describe how whiteout occurs
- In absence of direct light, there are no shadows and contrast b/t objects is reduced.
- Our ability to 'see' relies on this and therefore our perception in 3D is what is limited.
102
What are the effects of whiteout on the observer (6)
1.Lack of shadows/contrast/distance perception = Loss of perspective
2. Reduced horizon definition/false horizons
3. Loss of sense of direction
4. Vertigo
5. Spatial disorientation (trust your instruments!)
6. Eye strain
103
What are the three main influences on NZ WX
1. The surrounding ocean environment with high average water vapour content
2. High relief, with strong orographic effects, giving bigger contrasts b/t E and W than N and S
3. The countries location in a region of travelling highs and Lows with strong Westerlies and variable WX
104
WX in High Westerly Index flow over NZ
- Poor flying conditions experienced on West coast of both islands.
- Dry but turbulent WX in East of both islands
105
WX in Low westerly index flow over NZ
- Upper East of both islands poor WX conditions are experienced.
- Fine in West of both islands.
106
Tarbuck and Lutgens model outline
Tropical or Hadley Cell @ equator (air rises @ equator and sinks again at 30deg S)
Mid latitude Cell (NZ lies here AT 36 deg S) (All air here flows south)
Polar front (Lifts air up and over Polar cell)
Polar cell
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Define the Walker Cell
A semi permanent High pressure system in Eastern pacific off of the west coast of Peru. Formed and maintained by the cold Peruvian current that flows from the Southern Oceans up the West coast of South America. (waxes and wanes as travelling highs pass through the area, and when the current strengthens, Cell increases in size and vice versa).
Has a big impact on Southern Hemisphere WX
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What is the ITCZ?
Inter tropical Convergence Zone.
Formed by the clash of the SE trade winds from the SH with the NE trade winds from the NH along the northern side of the equator.
Collision results in air rising and increased TS activity.
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What is the SPCZ?
The South Pacific Convergence Zone.
Formed by the mid - latitude westerlies clashing with the Northerly Outflow from the Walker Cell.
Collision results in air rising and increased TS activity (not quite as intense as ITCZ showers) This area is where Tropical Cyclones are created in the South Pacific
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What is El Nino
Also known as a max negative Southern Oscillation.
Occurs when the Peruvian current falls and is replaced by a warmer sea SFC temp that lowers eastern pacific pressures. The Walker Cell 'Shrinks' and the SPCZ migrates East = more TCs in the Cook islands
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What is La Nina
Also known as the max positive Southern Oscillation. Occurs when the Peruvian Current becomes colder and stronger, lowering SFC sea temps and increasing eastern pacific pressures. The Walker Cell increases in size and the SPCZ is forced towards NZ = More TCs in NZ.
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What are Monsoons
A cross - equitorial wind flow that is enhanced by sea breeze effects, causes extreme rainfall.
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Why do SCWDs freeze slowly on impact (Clear ice)
Due to the release of latent heat, causing the freezing process to last longer than normal.
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Advantages of Polar orbiting satellites (3) compared to Geostationary satellites (1)
Polar:
1. Frequent coverage at high latitudes obtained
2. Higher resolution achieved with lower orbit
3. Accurate data with satellite more overhead
Geo:
1. Frequent coverage at low and mid latitudes
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Validity of High Level wind charts
Issued four times daily (0000, 0600, 1200, 1800 UTC).
Each chart has a true validity of +/- 3hrs of the stated times.
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Up to what depth and how restricted can visibility become in a blizzard?
Up to a depth of about 100ft above the SFC, visibility can be reduced to zero
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Can volcanic ash be seen on radar/satellites
Can be seen in satellite imagery, however it cannot be seen on radar as it is dry.
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What happens to pressure when a cold front passes through an area?
Sharp pressure rise in the colder, heavier air mass following the front.
119
How is WX for OH, Wanganui and Palmy affected by winds from a particular sector
- If winds are within the 260 - 310deg sector and moist, OH gets poor WX
- If winds are sightly further South of Wanganui, OH will get poor WX, Palmy will be OK (but will get terrain channeling from any Easterlies)
- Winds from 310, Wanganui will be sheltered.
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Avoidance and alleviation steps for airframe icing
- Arrange to avoid FZL during planning stage
- Use your WX radar and avoid active Cb cells
- Avoid flight parallel to Mountain range in updrafting areas of Lenticularis clouds
- Deicing and Anti-icing equipment
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Enhancing factors of clear ice
1. If the source air is moist
2. Forced lifting (via frontal lifting, convection, orographic or lee waves)
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Prevailing visibility?
Max vis covering at least half the horizon
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GS
VC
FG
BR
HZ
RASN
DR
GS: largest hail <5mm, otherwise GR
VC: vicinity =8-16km from AD ref pt
FG: vis <1000m
BR: vis 1000-5000m
HZ: vis >5000m but not water/ice
RASN: sleet
DR: blowing below knee height
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Tempo?
Temp chge lasting less than 60mins during specified time frame, condxns less dominant than OG forecast
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NOSIG?
Nil sig change expected within 2hr forecast
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WS R?
Wind shear on designated RWY up to 1600t agl
127
ARFOR?
Area forecast
Wind & wx up to 10000AMSL
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Layers of the atmosphere?
TSMT
Troposphere
Tropopause
Stratosphere
Mesosphere
Thermosphere
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What is diurnal variation
Affected by?
Daily variation on sfc air temp
- SFC type (land absorbs sun/water doesn’t)
- Location
- wind (calm = no mix of air/less molecules to share heat changes)
- cloud (reflects sun radiation)
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Typical diurnal temp variation
Coolest just after sunrise (sun low, land coolest)
Hottest 2hrs after midday (sun high, land max heat)
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4 causes of localised pressure variations
1. Lee trough (wind build up on windward side = low pressure in lee)
2. Thermal or heat low (heated/cooled air masses)
3. Diurnal variation (heated/cooled air masses)
4. TS (up & downdrafts)
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Geostrophic wind - describe
Air starts to move toward low pressure under pressure gradient force. As it accelerates, Coriolis force (proportional to speed), increasingly pulls air to the left (SH), eventually, flow is parallel to isobars.
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Dew point?
Temp required to saturate air (dew/mist/fog forms)
