MET 2 EXAM DECK Flashcards
1
Q
What are the two types of Satellites?
A
Polar Orbiting
Geostationary
2
Q
**Period of coverage: Polar Orbiting Satellites vs Geostationary
A
PO: Passes over poles every 105min, complete coverage of earths SFC every 12hrs
GS: Image provided every 10-15min 24/7
3
Q
**Advantages of Polar Orbiting Satellites
A
- Frequent coverage at high latitudes
- Higher res achieved with low orbit
- Accurate data with satellite overhead.
4
Q
**Disadvantages of Polar Orbiting Satellites (2)
A
- For Lower latitudes it takes 12hrs for satellite to reach overhead again. (We have 2x satellites = 4x images per day)
- Doesn’t provide continuous view of one location
5
Q
**Advantages of Geostationary Satellites
A
- Frequent coverage of low/mid latitudes
6
Q
**Disadvantages of Geostationary Satellites
A
- Distortion at higher latitudes due angle of viewing
- Lower res
- Costlier to deploy
7
Q
**Compare the advantages of IR vs. VIS imagery
A
IR imagery: relies on temp of cloud to create image - NIGHT OR DAY.
VIS imagery: Relies on reflected light (intensity is subject to albedo) to produce an image, usually higher res also - DAY ONLY.
For both: (White = high alt, Grey = low alt)
8
Q
**How does IR imagery work?
A
Utilises the IR spectrum where the radiance at a particular wavelength is proportional to the temperature of the emitting surface.
9
Q
How does Cloud tops (CT) imagery work?
A
Cloud tops are assigned a colour depending on the temperature band it falls under. Altitude of the cloud tops can then be identified;
High: Purple/red/yellow
Mid: Blue/Green
Low: Greys
10
Q
NZ wx radar network
A
10x wx radar sites
Full normal mode 300km radius
Doppelar mode 150km radius
11
Q
In basic terms how does the wx radar work
A
Microwaves emitted from radar, strong echoes received from precip droplets.
Intensity of echo relative to rainfall rate
12
Q
What are the 7 common radar problems
A
- Attenuation/radar shadowing
- Ground/sea echoes caused by refraction of radar beam due inversion
- Sea clutter (side lobes pick up high sea states)
- Radar elevation (min elev = 0.5deg above horizon. means 16km above SFC at 300km)
- False echoes at sunrise/set (sun radiation picked up)
- Bugs
- Interference from radio signals
13
Q
In basic terms, how does Doppler radar work
A
By measuring the phase shift b/t tx and rx signals, target motion & reflectivity can be assessed.
(in the case of wx radar, microbursts can be analysed if within doppler range)
14
Q
What are the four methods of horizontal air flow in the atmosphere
A
- Translation
- Divergence
- Convergence
- Deformation
15
Q
Define Translation
A
Where a body of air is moved without rotation or altering of its shape or volume
(Nil upwards motion)
16
Q
Define Divergence & Convergence (-ive DIV)
A
DIV: Expansion horizontally
CONV opposite to ^^
NET INFLOW MUST MEET NET OUTFLOW.
17
Q
Define Deformation
What is present for it to occur?
A
Body of air changes shape.
Confluence and diffluence both present.
18
Q
When would CONV or DIV occur?
What causes this?
A
CONV: Air decelerates and/or there is confluence.
DIV: Air accelerates and/or there is diffluence.
Changes in absolute vorticity
19
Q
Confluence vs. Diffluence
How do they affect CONV & DIV?
A
Confluence: Air coming together
Diffluence: Air moving apart.
Confluence & Diffluence may ENHANCE CONV & DIV, but they can also exist without.
20
Q
What must occur if there is CONV at the surface?
Reverse?
What is this?
A
Ascent of air & DIV aloft
DIV at SFC = subsidence & CONV aloft.
The VERTICAL component of circulation, results in formation of cloud etc.
21
Q
**What is vorticity & when does it occur?
A
Vorticity is the amount of rotation at a given point
Occurs where flow is curved or there is shear
22
Q
**Equation for absolute vorticity?
A
Relative vorticity + Earths vorticity = Absolute vorticity.
23
Q
**What is relative vorticity? What is it the the sum of?
What is it dependent on?
A
It is vorticity relative to the earths SFC.
Curvature and shear vorticity.
The shape and position of the upper air pattern.
24
Q
**How does earths vorticity affect absolute vorticity?
A
Earths vorticity is always cyclonic (CW in SH, ACW in NH)
It also swamps Relative vorticity and increases at higher latitudes.
Therefore absolute vorticity is always cyclonic.
25
**How does a change in absolute vorticity affect CONV vs. DIV?
Increase in AV = CONV
Decrease in AV = DIV
26
**Define an Anticyclone
- Area of relatively high px relative to the region surrounding (highest px in centre)
- Surrounded by at least one or more circular isobar
- ACW in SH
- DIV at SFC = subsidence from aloft
- Nil predetermined px rqd.
27
**How is the subtropical belt of Highs formed (WARM Anticyclone?
How does it move in summer vs winter?
1. Gen circulation causes air at equator to rise, it then flows south & CONV along the lines of longitude
2. CONV & Cooling aloft = subsidence to the SFC @ ~25-30deg south
3. ^^ results in high pressures at SFC = subtropical belt.
(DALR means warm air, therefore warm Anticyclones)
Mean pstn shifts north in winter, south in summer
28
What is created due subsidence aloft?
Altitude? Why?
Subsidence inversion ~3000-8000ft (stops at this lvl due weak convection at SFC which opposes subsiding air)
29
What enhances warm anticyclones wrt upper air pattern
Increase in absolute vorticity in upper atmosphere (increases CONV within the jetstream passing overhead & strengthens downward motion)
30
**Draw the general circulation
31
**Ident the typical wx characteristics associated with warm anticyclones
- NE 1/4: fine wx, light winds, good vis, Summer TS possible.
- West 1/2: "dirty". Anticyclonic gloom due stable atmosphere, vast areas of St cloud, reduced vis due aerosol entrapment.
- Top NW: Poor wx, FG and/or low cloud, poor vis in light RA & DZ.
- Far east: weak convection due cold advection = Partly cloudy, slightly unstable, light SH, Good vis otherwise.
32
Describe how anticyclonic gloom forms in the western portion of a high pressure system
Subsidence inversion is stronger, plus more aerosols as the high moves further East = HZ & Poor Vis
Northerly flow = stable & adds more low level moisture to flow
Stratus type cloud common.
33
**How does a cold anticyclone form
Example?
Driven from a cold SFC.
- Ground cools & air above also cools & becomes denser. SFC px rises & Anticyclone forms.
Central Otago.
Continental Siberian high. (semi-permanent)
34
6 hazards associated with anticyclones
1. Convective showers to the East (Cu & SHRA/GS)
2. Extensive low cloud (100-300ft), DZ/-RA & poor vis in West side
3. High winds & turb at fringes.
4. Haze (Due trapping beneath inversion)
5. Fog (centre due radiational cooling under clear skies)
6. Summer TS
35
**What is an airmass
A large body of air whose physical characteristics, esp temp & humidity, are approx the same, level for level, over large horizontal distances.
36
**What is a front
When does it occur in NZ?
The boundary between airmass with different temp & moisture characteristics.
Usually associated with poor flying condxs.
Occurs in NZ when mT and mP airmasses come together.
37
**What two airmass source regions does NZ experience
mT: Maritime Tropical (moist warm air from the North)
mP: Maritime Polar (moist cold air from the South)
38
**What is a cold front
6 Characteristics?
Cold airmass undercuts slower moving warmer airmass.
- Fast moving; 15-40kts
- Marked temp drop as front goes through
- Abrupt wind chg from Northerly 1/4 to SW 1/4
- Sharp px rise in colder, heavier airmass behind front.
- Cu clouds with SH of RA, GS or SN.
- Narrow band of Precip just prior to wind chg.
39
**What is a warm front?
6 Characteristics?
Warm air forced aloft by slower moving cold airmass underneath.
- Slow, 5-15kts
- Temp rise behind front in clearing wx.
- Wind chg from NNE to NW (not as marked)
- Extensive sheet of St type cloud, slowly thickens & lowers 100s of kms ahead.
- RA falls from Ns & As for a long time before wind chg.
- Poss low St or FG in saturated air below As & Ns due continuous rain.
40
**What is an occluded front
Types?
4 characteristics?
Cold front catching up to a warm front, weak characteristics of both types of airmass present.
2 types: cold & warm occlusions.
- Extensive cloud sheet of warm front type, thickens & lowers as front approaches
- Long periods of RA with embedded heavy SH
- Wind chg similar to cold front type
- Temp may drop slightly in cooler air behind front.
41
**What is a stationary front
Why do they occur?
Any front that has slowed to <5kts across the ground
Running into blocking High px system or area with slack px gradient
42
What are active fronts characterised by? (4)
- Large temp gradient across the front
- Front is moving at >30kts across SFC
- Front is located under an area of upper level DIV.
- Polar frontal Jet associated with the front has a large N to S component to its flow.
43
Cold front - associated wx?
Advancing cold air forces warmer less dense air rapidly upwards.
= Condensation, Cu, Cb, TCu (often embedded)
44
How does the location of a cold front in comparison with a Low pressure system affect the wx produced?
- If close to Low, cloud sheet is deep & active (due to much upper level DIV enhancing upward motion)
- If further away, there is usually subsidence aloft (due upper lvl CONV), the cloud band will be narrower & shallow in comparison
45
**Describe cold air Advection (Southerly mP flow onto NZ)
- Cold, moist air moving N over progressively warmer sea SFC
- Airmass warms up at SFC
- Increased instability = convection
- Condensation occurs, Cu, TCu and Cb form.
- Results in SHRA/GS/SN/ RASN, poor vis in SH, and mod-severe turbulence.
46
**Describe warm air Advection (Northerly mT flow onto NZ)
- Warm, moist air moving South over cooling SFC.
- Airmass cools at SFC
- Inversion develops & stability increases
- Any lifting & resultant condensation = St type clouds forming & poss very low cloud bases. (if no lifting, Advection or sea fog can occur at SFC)
- Resulting in continuous RA or DZ, poor vis & light to mod turbulence (Sev if strong px gradient exists)
47
Define a Depression
An area of relatively low px surrounded by areas of high px. Clockwise winds.
Surrounded by at least one circular & concentric isobar.
48
**How are depressions formed (with relation to convergence & divergence)
What forms due to this process?
- CONV at low level caused by friction near SFC bending wind across isobars towards low px
- DIV aloft caused by decreases in absolute vorticity.
NOTE: THESE TWO PROCESSES ARE INDEPENDENT OF EACH OTHER.
- Upward motion as a result of the above.
- Thick cloud formation & precip due upward motion. Generally concentrated about the fronts.
49
Describe the airflow in the upper atmosphere wrt Troughs vs ridges.
Trough:
Cyclonic Rel Vort + Earths cyclonic Vort = MAX CYCLONIC Absolute Vorticity = CONV.
Ridge:
Anticyclonic Rel Vort + Earths Cyclonic Vort = MIN CYCLONIC Absolute Vorticity = DIV (due slowing down of rotation)
50
**Draw a diagram of the upper air flow.
Where would the High & Low pressure systems be?
High Px: Underneath the area of CONV
Low Px: Underneath the area of DIV
51
What are 4 factors that enhance upward motion?
(wrt upper air pattern)
1. Increased sharpness of the curvature of upper atmosphere trough or ridge
2. An increase in shear vorticity (e.g. a jet passing over)
3. Increased Diffluence (if isoheights spread out downstream of upper trough)
4. Cloud development (latent heat release = destabilisation & updrafts)
52
**What does westward tilt mean?
Stacked?
SFC Low px system/column of air has a westward tilt towards the Upper level trough.
Becomes stacked as the upper air pattern moves eastward, and the upper trough arrives overhead of the SFC Low. At this point it will be at its maximum intensity & will subsequently decay.
53
Depth of Warm vs. Cold high pressure systems
Cold: shallow, 3-5000ft
Warm: full depth of atmosphere.
54
What is a Lee Depression
Formed in strong wind condxns.
WW side has a build up of air & resulting localised area of high px.
LW side has a corresponding decrease in px & resulting orographic trough.
Sometimes lee trough can be cut off at low levels, resulting in Lee Depression.
55
How does a thermal Low develop?
DIV at what alt?
1. Sun heats land mass (hot summer days, light winds)
2. Air heated from below & becomes less bouyant.
3. Convection = upwards transfer of air.
4. DIV at 2-5000ft AGL
Results in SFC low being formed.
56
Wx Associated with Leeward trough?
- Strong winds & mech turb, lee wave activity
- Likely sig cloud & vis problems due precip on WW side.
- LW side = dry & high cloud bases
- Large QNH changes over short dist (WW ridge/LW trough)
57
Wx associated with Thermal Low?
1. Convective turb in thermals
2. Poss PM CBs with TS, SHRA/GS
3. Warm temps & low px = higher DA. (reduced perf)
58
Describe how a depression is effected when crossing a mountain barrier
1. Low level circulation appears to stop,
2. Upper trough & associated upper DIV continue to move unimpeded.
3. SFC cyclonic circulation redevelops on lee side. (new depression develops)
Original low on WW side slowly decays.
59
Tropical Cyclone Properties (6)
1. Warm core, formed over oceans >27deg
2. Smaller but more intense than mid-lat storm, winds >150kts
3. Several spiral bands of +RA (rather than fronts)
4. Named
5. Tend to form 5-15deg N/S.
60
**What is a thermal wind?
Horizontal temp gradient within a layer of air creates
px differences within that layer. (therefore wind)
Because the change of wind with height (windshear) is due mainly to temp diffs, we call them thermal winds.
61
**How to calculate thermal wind?
Draw a diagram
Using vector addition between the geostrophic wind at a lower level and the geostrophic wind at an upper level;
Upper wind = SFC wind + thermal wind.
62
**Define a Jet stream
Where would you expect them?
A region of strong winds in excess of 60kts (sustained)
Wherever there is a strong temp gradient.
63
**Describe the main mechanism behind the polar jet stream?
- Equator receives more heating than the poles
- Temp gradient b/t Eq & Poles = greatest "slope" (gradient) at Mid latitudes.
- Therefore westerly is strongest at Mid Lats.
At times, most of these temp differences are confined to narrow frontal zones = Polar Front Jet.
64
**Polar Frontal Jet Characteristics (6)
- Located ~50-60deg South.
- Driven by thermal wind across frontal zones.
- Not usually continuous around the globe
- Always W'ly, Often have a large N/S component
- Found at FL300 in warm air, a few deg poleward of SFC front
- Max 80-100kts (NZ), can reach up to 200kts
65
**Sub Tropical Jet Characteristics (5)
Driven by?
- Driven by conservation of angular momentum as air exiting equator is increasingly deflected East
- Mostly continuous around globe.
- Usually located above sub tropical belt of Highs (25-35deg South)
- Very zonal, only a few deg N/S of westerly
- Found at ~FL400
- Max 80kts (summer) & 120kts (winter) in NZ. Can reach up to 200kts.
66
**Cloud associated with Jets;
- Sub tropical
- Polar jet
- Sub tropical: Cloud free on poleward side of Jet
- Polar Frontal: Cirrus close to tropopause on Eq side & dense cirrus poleward side
67
**Define CAT
Chaotic motion caused by eddies resulting from momentum, temp or energy tsfr in the atmosphere.
(e.g. large horizontal/vertical temp chgs associated with jet that results in W/S)
68
Where would you expect CAT in a Jetstream?
Most severe on polar side of the jet, both above & below the core. (Esp at exit & entry to the jet)
69
What are the 5 types of aircraft icing
1. Rime ice
2. Glaze ice
3. Mixed
4. Hoar frost
5. FZRA/FZDZ
70
What is required for Aircraft icing?
Freezing Nuclei (Aerosol that H20 can deposit on to - Aircraft can be this nuclei)
SCWDs: H20 that is colder than 0deg C due lack of freezing nuclei.
71
At what temp have all SCWD completely frozen out?
-40deg C
72
**How does Rime Icing form?
Enhanced by?
- Forms at high alts & at much colder temps.
- SCWD are much smaller & less numerous.
- SCWD freeze instantly on collision, releasing little latent heat & trapping small pockets of air.
= brittle & easy to dislodge
Warm fronts
73
**Rime Icing - temperatures
Generally: 0 to -40deg
Commonly: -15 to -30deg
74
**What cloud would you expect rime icing in?
Sc, St, As, Ac
75
**How does glaze icing form?
-SCWD Large & numerous
- Freezing process is not instantaneous due to release of latent heat which slows it down.
- Droplet spreads back over the wing before freezing fully.
= no airbubbles results in strong adherence, heavy clear ice that is hard to see.
76
**Glaze icing - temperatures
Generally?
Most common?
Worst?
Exception?
Generally: 0 to -20deg
Commonly: -3 to -12deg
Worst: -5 to -8deg
-12 to -25 in updrafting portion of wave cloud.
77
**What cloud would you expect glaze icing in?
Cb, TCu, Ns, updrafting portion of Ac lenticularis
78
**How does Mixed ice form?
How should it be treated
Combination of both clear & glaze icing.
For this to occur, clouds must contain a large range of SCWD sizes.
Means both Cu (large) & St (small), type clouds exist
TREAT AS CLEAR ICE
79
**What clouds would you expect mixed icing in?
TCu/Cb embedded in layers of Sc, As, Ns
80
**Mixed Ice - temperatures?
Generally: -10 to -25deg
Commonly: -10 to -15deg
81
**Hazards of icing to aviation?
- Changes to aerodynamics (increase in weight & drag = reduction in lift & tailplane/main plane stall, INCREASE IN STALL SPEED)
- Damage to trailing SFCs of a/c due ice falling off of forward SFCs.
- Ice ingestion into engines
- Intake/prop/pitot & static vents icing
- Control SFCs: freezing solid/uncommanded full deflection.
- Uneven ice distribution = severe vibration & structural failure.
- Poor radio reception & vis due ice build up on aerials/windshield.
82
How to avoid icing? (6)
- Preflight: Avoid at planning stage (Sigwx/Sigmet/FZL)
- In flight: wx radar/OAT
- Avoid flight in Cb, TCu, Ns & updrafting portion of Ac lenticularis (in temps -25 & warmer)
- descend/ESC laterally. If unable to descend, climb as high as poss.
- Fly >500kts (frictional heating & compression = warming)
- Deicing/Anti icing equip.
83
Enhancing factors for Glaze icing
1. Source air is moist (particularly from sub tropics)
2. Air is forced to rise due;
- Frontal lifting (esp Warm)
- Orographic lifting
- Lee Waves
- Convection (TS type)
84
**3 Conditions required for TS development?
1. A trigger mechanism to initiate lifting (orographic/convection/ widespread ascent)
2. An adequate supply of moisture at low levels
3. Conditional instability through depth in the atmosphere.
85
3 types of Airmass TS?
1. Convective
2. Orographic
3. Nocturnal (common in tropics)
86
3 Types of Frontal TS?
1. SFC fronts
2. SFC trough
3. Upper Trough
87
**How long is the lifecycle of a TS?
1.5hrs- 2hrs, ~30mins per stage.
(FOR UPRIGHT, STATIONARY CBs)
88
**Describe the 1st stage of TS development
Cumulus stage
- Updrafts only
- Mass latent heat release due cloud formation.
- Light to Mod Turb, Icing can reach Sev due large amount of SCWD being carried aloft by updrafts.
- Most other hazards yet to occur.
- Light rain is possible.
89
**Describe the 2nd stage of TS development
Mature stage
- Up & downdrafts
- Signified by onset of Precip at SFC & Anvil as droplets spread out beneath tropopause.
- Any of the 8 hazards associated with Cbs may now exist.
90
**Describe the 3rd stage of TS development
Dissipating stage
- Anvil starts to become glaciated, clear sign of cirrus development
- Updrafts cease & hazards weaken/dissapear.
- Bottom 2/3 of cloud will dissipate leaving benign cirrus & anvil.
91
**List the 8 hazards associated with TS?
1. Sev Turb
2. Sev Icing
3. Microburst
4. Gust front
5. Electrical Phenomena
6. Hail
7. Tornadoes
8. Poor Vis
92
**Describe the formation of hail within TS?
- Initial formation of ice embryos
- Ice crystal carried in cycle of up & down drafts.
- Grows due coalesence with SCWD.
- High level in cloud = rime ice layer
- Low level in cloud = glaze ice layer.
- Once hail stone has grown to a size where it can no longer be supported by updrafts, it will fall to SFC.
93
**Avoidance of TS? (5)
1. Plan to avoid/have an alternate track
2. Do not fly under orographic TS
3. Cross a line of TS at right angles.
4. Use wx radar to assist in avoidance.
5. Avoid flying within 5nm downwind of the anvil (hail)
94
What is a microburst
Mature stage Cb,
Localised, short lived, severe wind pattern driven by extremely strong downdrafts from dense rain-cooled air. Can exceed 100kts VV.
Can be dry or wet.
95
What is a gust front
Characterised by?
Impact?
Associated with microburst.
Leading edge of cold dense air spreading out horizontally at base of Cb.
Sudden wind chg & lowered temp have characteristics of a cold front.
Characterised by roll cloud
For a/c taking off = Sig W/S & air density changes
96
**Describe the wind flow in a NW'ly over the South Island
- Wind above ~3000ft rises up & over terrain.
- Wind below ~3000ft deflected by ranges to become NE'ly (Barrier Jet)
- SFC winds head down river valley (terrain channeling)
- Low level wind deflection around farewell spit & through cook strait.
97
Factors that influence wind flow over mountain ranges? (5)
1. Wind strength
2. Angle of wind flow near ranges
3. Shape of the mountain range
4. Stability of the air
5. Vertical profile of wind speed & direction
98
**What are the requirements for lee wave development (5)
1. Wind flow within 30 deg of perpendicular to ridge line.
2. At least 20kts at ridge top level
3. Wind speed increasing with height.
4. Little variation of wind direction with height.
5. A stable layer in the atmosphere about ridgetop level (to provide restoring force)
99
What does wavelength depend on in lee wave formation?
The stability and speed of the air
100
What is a rotor zone
An area of severe turbulence in the lee of a mountain, formed in between wave columns in rotating air.
Straggly cloud only forms if sufficient moisture is present.
101
**What is rotor streaming?
Requirements for rotor streaming? (2)
Lee waves will not form, single rotor forms at ridge top level. Not anchored by wave, will migrate downstream.
- Wind near perpendicular to ridge line
- Strong winds at ridge top height but decreasing above (e.g. strong E'ly below, W'ly above)
102
**Main features of lee waves? (7)
- Bands of lifting & sinking air parallel to range
- AC Lentics & rotors if sufficient moisture
- Sev turb in rotors
- High level CAT if Jet present
- Smooth flight in wave systems above friction layer.
- Downdrafts can reach ground causing local strong winds (hyd jumps)
- Sev icing in updrafting Ac Lentics.
103
What is a hydraulic jump?
What is needed for it to Occur?
NZ E.g.?
Dangerous phenomenon that occurs when extremely strong down slope air meets slower downstream winds = sudden "jump" in wind.
High stability, strong wind but minimally sheared with height.
Strong NW against Southern Alps ahead of a front.
104
**Draw a basic diagram of lee wave development
105
**How does terrain influence lee wave development? (3)
Multiple ranges can either cancel out the wave, double the amplitude or cause counter rotating flows in adjacent valleys
106
**What is a Fohn wind?
When would you expect it?
A warm, dry, very gusty wind blowing down the lee side of a major mountain range.
(Canterbury Plains in Strong NW'ly)
107
**How does a Fohn wind develop?
1. Air rises on WW side of range.
2. Cloud forms, LH released, Air cools at SALR.
3. If rain occurs on WW side, water vapour in air is reduced.
4. Air on LW side then warms at DALR for a greater distance = very warm & dry air in lee
108
Hazards of Fohn winds?
LW - lee wave activity/turb in rotor zone/up & down drafts/very warm temps (can affect perf)
WW - Very Low cloud bases/ heavy precip/poor vis.
109
What is the Fohn Gap?
Band of clear skies in the lee of the ranges in descending air of the wave system.
110
**What are the two features of flight within rotor streaming?
1. Sev turb in rotor zone in the lee, about & below ridge top level.
2. Relatively smooth flight above ridge level
111
What are the 4 dangers of flying across ranges in lee waves?
1. Strong Downdrafts
2. Rising ground
3. Low G/S
4. Risk of rotors = sev turb
112
List the dangers of Volcanic Ash to flight (11)
1. Jet engine flameout
2. Severe erosion of fanblades
3. Blocked pitot tubes
4. Poor radio reception
5. Poor vis (windshield pitting)
6. Engine oil contamination
7. Loss of cabin px
8. St elmos fire
9. Light dust entering cabin
10. Wet ash on RWY - slippery
11. Paint "sandblasted" off aircraft.
113
**NZ 2 most recently active volcanoes
Mt Ruapehu, White Island,
114
**How to get out of VA?
Exit ash cloud as fast as possible; 180deg descending turn (allows us to avoid the use of full power)
115
**Where does NZ sit in the general global circulation?
Mid Lat cell, Below sub tropical high px zone (30 deg Sth), above polar low px zone (60 deg Sth)
116
**How does SFC px change before & after cold front?
Px decreases before front due warm air ascending.
Sharp px rise in colder, heavier airmass behind front.
117
**What 4 conditions produce blowing dust?
- Extended dry period
- Marked instability
- Strong SFC winds
- Enhancement by 'dry' cold fronts
118
**At what temps is airframe icing an issue, why not when it is extremely cold?
0 to -40deg (IN CLOUD)
At colder than -40deg all SCWD have frozen out, only ice crystals exist in the atmosphere.
119
**BLSN/blizzard: what is the depth & associated vis reductions dependent on? (3 requirements)
1. Age of the snow (10kts new snow, 40kts old)
2. Speed of the wind
3. Stable layer above snow SFC to limit vertical displacement.
120
**What is whiteout?
An optical effect caused by diffuse illumination (light that comes from all directions with equal intensity, so no objects cast shadows)
121
**Result of whiteout on observer?
Features become indistinguishable from their background.
Lack of SFC & horizon definition.
(loss of sense of direction/disorientation etc.)
122
**Conditions needed for whiteout to occur?
- Uniform cloud cover
- Snow or ice covered SFC
123
**What occurs if glaze icing is left to form?
Horns/ridges my build up at rivet/joint lines & on Leading edges.
Airflow across wing severely disrupted, reducing lift.
124
**Radar images: Precip returns;
1. Thick even layer, blues & yellows
2. Localised individual areas, blues & yellows
1. St type cloud, cont mod to heavy intensity precip (DZ/RA)
2. Cu type cloud, mod to heavy convective SH activity.
125
** Draw Diagram representing Relative vorticity
126
**Draw a diagram of cold vs warm occlusions
Warm vs. cold is based on the temp gradient between the two fronts.
127
**Draw the global circulation diagram
128
**How do Orographic troughs form?
Formed in strong wind conditions in lee of mountain range.
As an airmass is forced over/around a mountain barrier there is a build up of air on the WW side = high px.
Corresponding drop of px in lee = orographic trough
129
**What is earths vorticity
Fixed & arises from the shear induced by earth rotation, increases with latitude
130
**3 main factors influencing NZ climate
1. Maritime environment with high ave. water vapour content
2. High relief topography = sig orographic effect with large contrast b/t W-E, N-S
3. Location in a region of travelling highs and lows with strong W'lies and variable wx.
131
**How does a high westerly index affect NZ
- SFC W'lies over NZ & upper level W'lies
- Wx & px systems move relatively quickly W-E across NZ
- West side of NZ gets most of the precip & bad wx
132
**How does a low Westerly index affect NZ?
- SFC East/Northeasterlies over NZ & Upper level N/S wind components
- Wx & px systems move relatively slowly across NZ E-W
- Rain & low cloud on eastern side of NZ
133
**Define a Monsoon
Where would yo expect one?
- Cross equatorial flow of trade winds associated with seasonal chgs in equatorial trough & ITCZ
- Large amounts of RA & cloud associated
Aus, Southern Indonesia, Northern Asia
134
**Describe the ITCZ
Region formed by clash of SE trade winds from SH with NE trade winds from NH.
Results in upwards motion over vast area, accompanied by prolonged +RA & violent TS activity
135
**Describe La Nina
Colder & stronger peruvian current, intensifies the walker cell, forces SPCZ towards NZ.
results in Low westerly index situations
136
**Describe El Nino
Peruvian current fails at the SFC, replaced by warmer temps, walker cell shrinks & SPCZ migrates further east towards cook islands.
Results in High westerly index situations
137
What is the walker cell
A semi-permanent high pressure system off the coast of Peru.
Formed & maintained by the cold peruvian current.
