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Met1 Flashcards

1
Q

Wind flow around a high?

A

Anticlockwise

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2
Q

Wind flow around a low?

A

Clockwise

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3
Q

List features of a weather chart

A 
Isobars
Depression - low
Anticyclone - high
Ridge of high pressure
Trough of low pressure
Col
Fronts
Tropical cyclone
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4
Q

What is a col?

A

A region of almost even pressure between two opposing highs and lows

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5
Q

Types of fronts?

A

Cold, warm, stationary, occluded

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6
Q

Types of briefings you can access

A 
TAFs - departure and destination, alternate
METAR/SPECI's
Aviation Area winds
GRAFORs
GNZSIGWX
SIGMET
ROFORs
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7
Q

What is the geogrpahic coverage of a TAF?

In the Vicinity of?

A

8k radius of the aerodrome

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8
Q

3 Important points about TREND forecasts

A
  1. AK, WN, CH, WP, OH only.
  2. Forecast valid for two hours from issue
  3. TREND takes precedence over the TAF for the two hour period of validity
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9
Q

Descriptor and Visibility for fog, mist, haze?

A

FG - Vis less then 1000m
BR - Vis between 1000 & 5000m
HZ - Vis less than 5000m (reduction in vis not caused by water droplets)

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10
Q

Define TEMPO

A

Temporary changes each lasting less than 60 mins, weather before the change period will still be the dominant weather

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11
Q

What heights are used for AAWs vs TAFs/METARs?

A

AAW - feet AMSL

TAF/METAR - feet AGL

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12
Q

/// used for?

A

Missing groups or undefined cloud type in METAR AUTO

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13
Q

Relevance of dew point?

A

Fog will form if the air is cooled to this temp at constant pressure

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14
Q

NOSIG

A

No significant change for the next 2hr period

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15
Q

Why does the stratosphere have limited weather?

A

Minimal water vapour and winds here

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16
Q

Characteristics of the Troposphere?

A
  1. Always in motion
  2. Contains 75% of mass of the atmosphere in mid-latitudes
  3. Temperature generally decreases with height
  4. Height of troposphere is averages at 36,090ft at mid latitudes
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17
Q

What changes the height of the troposphere?

A

Variation due to thermal expansion/contraction
In summer its higher
Near the equator is high due to vertical expansion

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18
Q

List the gases in the atmosphere

A

Nitrogen ~78%
Oxygen ~21 %
Trace Gases ~1%

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19
Q

What are the ingredients of the atmosphere?

A
  1. Water Vapour
  2. Aerosols
  3. Carbon Dioxide
  4. Ozone
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20
Q

Describe ISA

A
  1. Mean Sea Level Temp 15°
  2. Mean Sea Level Pressure 1013.25 hPa
  3. Mean Sea Level Density 1225g/m3
  4. Temperature Lapse rate of 1.98° per 1000ft up to a height of 36,090ft, then isothermal at -56.5° up to 20km
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21
Q

What are some temperature scales?

A

Celsius, Kelvin, Farenheit

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22
Q

What is solar radiation?

A

Short wavelength radiation from the sun that warms the earth/atmopshere

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23
Q

What is terrestrial radiation?

A

Terrestrial is radiation emitted by the earth and its atmosphere to space

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24
Q

Which things effect daily temperature?

A
  1. Latitude
  2. Seasons
  3. Strong winds
  4. Wind direction
  5. Cloud cover
  6. Coastal or inland
  7. Surface type
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25
Q

Heat transfer methods? How do they work?

A

Radiation - Short wave EM radiation from sun
Conduction - heat transfer by contact
Convection - heat transfer by vertical movement of mass
Advection - horizontal heat transfer by wind

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26
Q

Earth heating processes? In/Out

A

Heat enters and leaves the earth/atmopshere via solar and terrestrial radiation respectively
Heat is then transferred within the atmosphere by conduction, convection, advection

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27
Q

What does the term albedo describe?

Define Specific Heat

A

The albedo of a surface measures the amount of incident radiation that is reflected
High albedo - lots of reflection (Snow)
Specific Heat - The quantity of heat energy required to raise the temperature of the unit of mass by 1° C.
Water - High specific heat
Land - Low specific heat

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28
Q

Seasons are based on what?

A 
Average temperature (Not on position of earth relative to sun)
Due to lag of balance between incoming and outgoing energy
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29
Q

Four different types of inversions?

A

Radiation, Turbulence, Subsidence, Frontal

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30
Q

How does a radiation inversion form?

A

Overnight in clear sky conditions
Earth loses long wave radiation at night - cools down
Air in immediate contact with ground is also cooled by conduction and low-level mixing
Induces an inversion

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31
Q

How does a turbulence inversion form?

A

Created at the top of the friction layer

Air beneath friction layer becomes turbulent, tumbling motion means some air rises and some falls
Wind of min 10 kts blowing over obstacles
Rising air expands, and cools adiabatically
Sinking air compressed and warmed adiabatically
Cooling in top half of layer offsets warming in bottom half
Creates steeper lapse rate
Sc can form if sufficient moisture present

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32
Q

How does a subsidence inversion form?

A

Due to initial formation process of a surface high
High level air just beneath tropopause converges and begins to sink
As more air converges, surface pressure starts to rise
Sinking air is subjected to increasing pressure and starts warming adiabatically

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33
Q

How does a frontal inversion form?

A

At any frontal surface where warm air is forced to rise over top of a layer of colder air

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34
Q

Effects of inversions on aviation?

A 
Formation of cloud
Visibility
Turbulence
Dew Point
Wind shear present
Aircraft performance
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35
Q

Which gases are the primary heat absorbers in the atmopshere?

A

Ozone, Oxygen, Carbon Dioxide

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36
Q

Define atmospheric pressure

A

The total weight of the column of air above the point where the pressure is being measured

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37
Q

Define pressure lapse rate

A

Air pressure must always decrease with increasing height

Approx 1hPa per 30ft

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38
Q

Define QNH

A

Aerodrome level pressure corrected to MSL using the ISA temperature lapse rate.
When set on the altimeter, the instrument will read the ALTITUDE of the aircraft above MSL

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39
Q

Define QNE

A

Pressure of 1013.2 hPa set on the altimeter

With QNE dialled up, instrument will read pressure altitude of flight level of the aircraft

40
Q

Define QFE

A

Aerodrome level pressure set on the altimeter

When QFE is set, intrument will read height of the aircraft above aerodrome level

41
Q

Define Transition Altitude and Level

A

Altitude 13000ft
Level FL150
Unusual to cruise between these altitudes

42
Q

What is the effect of decreasing MSL pressure, when the sub-scale is not reset?

A

High-Low, Watch out below

Will cause an altimeter under-reading

43
Q

What are some causes of variations in pressure over distance or time?

A

Lee Trough
Thermal or Heat lows
Thunderstorms
Diurnal Variation

44
Q

Three factors that contribute to high DA environments

A

Temperatures warmer than ISA
Pressures lower than ISA
High water vapour content

45
Q

Effect of High DA on aircraft performance?

A

Less engine power due to reduced oxygen content
Prop will generate less thrust because it is biting into lighter air
Wings will generate less lift because of less air molecules passing over the wing
- Longer TOLD
- ROC decreased
- Ceiling will decrease

46
Q

What type of general weather pattern would give negative pressure altitudes?

A

Temps lower than ISA
Pressures higher than ISA
Generally at lower airfields

47
Q

Define DA

A

Pressure altitude corrected for non-standard (ISA) temperature variations

48
Q

What is the rate of change of change of pressure?

A

30 feet per hPa

49
Q

What is the standard surface wind?

A

Ten minute average of speed and direction, measured at 10m above the surface

50
Q

What can SIGMETs be issued for?

A 
Thunderstorms
Tropical Cyclone
Severe Turbulence
Severe Icing
Severe Mountain Waves
Heavy Sandstorm or dust storms
Volcanic ash cloud and volcanic ejecta
51
Q

What do the following mean? INTSF, WKN, NC

A

Intensifying, Weakening, No Change in intensity

52
Q 
Define Cloud Amounts
SKC
NSC
FEW
SCT
BKN
OVC

NCD

A 
SKC - Sky clear
NSC - No significant cloud
FEW - 1-2 Oktas
SCT - 3-4 Oktas
BKN - 5-7 Oktas
OVC - 8 Oktas

NCD - Nil cloud detected by AWS

53
Q

Define Squall

A

Sudden increase in windspeed which must :

  1. Reach a wind speed of 22kts
  2. Must increase by 16kt
  3. Must last for one minute
54
Q

Define Gale

A

A 10 minute mean wind speed between 34-47kts

55
Q

Define Gust

A

Short term increase in wind speed lasting only a few seconds, must be greater than 10kts to be reported

56
Q

How do you estimate surface wind from the air?

A
  1. Beaufort scale to estimate by observing ground effects
  2. Ripples on water
  3. Wind lanes on water
  4. Cloud type or shape
  5. Cloud shadows
  6. Aircraft drift and apparent ground speed
  7. Cows
57
Q

What are the 3 forces on acting to create wind at ground level?

A
  1. Pressure Gradient Force
  2. Coriolis Force
  3. Friction
58
Q

What causes coriolis force?

A

The inertial force that acts on objects that are in motion relative to a rotating frame of reference

59
Q

What are 3 properties of the coriolis force?

A
  1. Acts at right angles, and to the left of motion in the southern hemisphere
  2. Strength is proportional to the wind speed
  3. Strength is proportional to the sine of the latitude (Zero at equator, Max at poles)
60
Q

Draw the geostrophic wind balance created in the southern hemisphere

A

PGF, CF and Friction force diagram

61
Q

How does friction affect surface wind velocity? Diagram

A

Diagram with friction, gives wind vector from high towards low pressure on angle

62
Q

Define Buys Ballots Law

A

If you stand with your back to the wind in the southern hemisphere, the low pressure is on your right

63
Q

Define windshear

A

A sudden change in wind speed and/or direction over a short distance, either horizontally or vertically

64
Q

What are the four categories of low-level turbulence?

A
  1. Surface friction
  2. Thunderstorms
  3. Temperature Inversions
  4. Frontal Activity
65
Q

What are the causal factors of turbulence?

A
  1. Convective
  2. Mechanical
  3. Wake Turbulence
  4. Clear Air Turbulence
66
Q

When would you expect wind shear associated with frontal activity?

A

When the temperature difference is greater than 5° across the front
OR
If the front is moving at more than 30 kts

67
Q

What do you need for a katabatic wind to form?

What is the NZ one called?

A

Clear nights
Sloping ground
Pressure gradient not too strong
- Greymouth Barber

68
Q

What do you need for a katabatic wind to form?

What is the NZ one called?

A

Clear nights
Sloping ground
Pressure gradient not too strong
- Greymouth Barber

69
Q

What are favourable conditions for a sea breeze to form?

Probably be able to describe too

A

A coastal situation (sea or lake)
Fine weather, especially summer time
Slack pressure gradient
The period mid-morning to late afternoon for onset

70
Q

What factors enhance terrain channeling?

A

Wind speed as a function of pressure gradient
The steepness and proximity of high ground
The stability of the atmosphere - a stable layer will enhance the effect

71
Q

Define dew point

A

The temperature at which a parcel of air must be cooled at constant pressure to become saturated

72
Q

Which processes take heat energy from the environment? (stored as latent heat)

A

Sublimation
Melting
Evaporation

73
Q

Which processes release latent heat to the atmosphere?

A

Deposition
Freezing
Condensation

74
Q

Why is relative humidity not useful as a measure of water vapour content?

A

When the RH changes, can’t be sure if its due to amount of water vapour or a change in temp

75
Q

Define Stable Air

A

Air displaced vertically is colder than the environment (and therefore heavier) and sinks back to its original level once the lifting force is removed

76
Q

Define Unstable Air

A

Air displaced vertically will become warmer than the environment (and therefore lighter) and will continue to rise when the lifting force ceases

77
Q

Define Conditionally Unstable Air

A

Air displaced vertically will have a temperature equal to the environment and will remain at the newly attained level when the lifting force is removed
(However certain conditions can mean that the parcel will become unstable and start to rise)

78
Q

Outline the adiabatic process

A

Parcel is forced to rise
Parcel subjected to less pressure
Therefore it expands
Expansion results in cooling

79
Q

What are the values of DALR and SALR

A 
DALR = 3° per 1000' (When RH is between 0-99%)
SALR = 1.5° per 1000' (When RH is 100% - Cloud)
80
Q

If ELR < SALR ?
If SALR < ELR < DALR?
If DALR < ELR?

A

Air is stable
Air is conditionally unstable
Air is unstable

81
Q

Which 4 factors cause air to rise in the atmosphere?

A

Convection
Orographic Lifting
Widespread Ascent (Low pressure or frontal system)
Turbulence

82
Q

What weather conditions would be associated with cold southerly maritime flow?

A 
Unstable conditions
Cumuliform cloud (Cu, TCu, Cb)
Showers of rain, hail, snow intermingled with patches of clear air
83
Q

What weather conditions would be associated with warm northerly maritime flow?

A

Stable conditions
Stratiform clouds (St, Sc, Ns, As)
Drizzle and/or rain

84
Q 
What do the following terms mean?
Cumulus
Stratus
Alto
Nimbo
Cirrus
A 
Cumulus - Pile (Heaped or puffy)
Stratus - Layer (Sheet-like)
Alto - Middle
Nimbo - Heavy rain
Cirrus - Curl (Streaky)
85
Q

List the ten basic cloud types

A

Ci, Cc, Cs
Ac, As, Ns,
Cb, Cu, Sc, St

86
Q

State the approximate cloud heights

A

High - 20,000’ to tropopause
Middle - 6,500’ to 20,000’
Low - Surface to 6,500’

87
Q

What are the limitations of a ceilometer?

A
  1. Sensor only samples cloud directly above the sensor (distant clouds missed)
  2. Small patch of stationary cloud will make the instrument report sky as overcast
  3. Approaching low cloud will not report until directly over sensor
  4. An overcast layer with a hole in it will report as no cloud detected
  5. Sensor cannot differentiate cloud types
88
Q

Be able to identify TCu and Cb

A

TCu - middle cloud, with absence of heavy rain

Cb - Heavy rain, anvil head

89
Q

How do you work out cloud base for convective and non-convective clouds?

A

Convective (TCu & Cb) Cloud base = 400x(Tsurface temp- Tdew point)
Forced lifting = 250x(Tsurface temp- Tdew point)

90
Q

What are three processes that lead to cloud disspation?

A
  1. Sinking of air
  2. Mixing with clear air
  3. Direct warming
91
Q

Define the precipitation rates of light, moderate, heavy

A

Light - Between a trace of rain and <2.5mm/hr
Moderate - >2.5mm/hr and < 10mm/hr
Heavy - >10mm/hr

92
Q

Describe the limitations of a forward scatter meter

A
  1. Prevailing visibility may be much better than reported if there is localised fog
  2. Prevailing vis may be very poor but not reported if not in the vicinity of the sensor
  3. Approaching poor vis associated with an isolated shower, rain or front will not be measured until it reaches the sensor
  4. Sensor cannot determine significant vis variations
  5. Most metservice sensors are limited to reporting 20km vis, it could be much better
93
Q

What is the effect of light/moderate/heavy precipitation on visibility?

A

Light - Little reduction
Moderate - 3000m - 10km
Heavy - less than 3000m

94
Q

What is the effect of fog and mist on visibility?

A

Fog <1000m
Mist >1000m
Haze < 5000m (Due to particles in air not water vapour)

95
Q

What are the requirements for radiation fog?

A 
Clear sky with a low humidity aloft to maintain it
Location over land
Overnight or early morning
High humidity near the ground
Light surface wind of 2-7kts

Met (1 decks)

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