Met1 Flashcards
(95 cards)
1
Q
Wind flow around a high?
A
Anticlockwise
2
Q
Wind flow around a low?
A
Clockwise
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
4
Q
What is a col?
A
A region of almost even pressure between two opposing highs and lows
5
Q
Types of fronts?
A
Cold, warm, stationary, occluded
6
Q
Types of briefings you can access
A
TAFs - departure and destination, alternate METAR/SPECI's Aviation Area winds GRAFORs GNZSIGWX SIGMET ROFORs
7
Q
What is the geogrpahic coverage of a TAF?
In the Vicinity of?
A
8k radius of the aerodrome
8
Q
3 Important points about TREND forecasts
A
- AK, WN, CH, WP, OH only.
- Forecast valid for two hours from issue
- TREND takes precedence over the TAF for the two hour period of validity
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)
10
Q
Define TEMPO
A
Temporary changes each lasting less than 60 mins, weather before the change period will still be the dominant weather
11
Q
What heights are used for AAWs vs TAFs/METARs?
A
AAW - feet AMSL
TAF/METAR - feet AGL
12
Q
/// used for?
A
Missing groups or undefined cloud type in METAR AUTO
13
Q
Relevance of dew point?
A
Fog will form if the air is cooled to this temp at constant pressure
14
Q
NOSIG
A
No significant change for the next 2hr period
15
Q
Why does the stratosphere have limited weather?
A
Minimal water vapour and winds here
16
Q
Characteristics of the Troposphere?
A
- Always in motion
- Contains 75% of mass of the atmosphere in mid-latitudes
- Temperature generally decreases with height
- Height of troposphere is averages at 36,090ft at mid latitudes
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
18
Q
List the gases in the atmosphere
A
Nitrogen ~78%
Oxygen ~21 %
Trace Gases ~1%
19
Q
What are the ingredients of the atmosphere?
A
- Water Vapour
- Aerosols
- Carbon Dioxide
- Ozone
20
Q
Describe ISA
A
- Mean Sea Level Temp 15°
- Mean Sea Level Pressure 1013.25 hPa
- Mean Sea Level Density 1225g/m3
- Temperature Lapse rate of 1.98° per 1000ft up to a height of 36,090ft, then isothermal at -56.5° up to 20km
21
Q
What are some temperature scales?
A
Celsius, Kelvin, Farenheit
22
Q
What is solar radiation?
A
Short wavelength radiation from the sun that warms the earth/atmopshere
23
Q
What is terrestrial radiation?
A
Terrestrial is radiation emitted by the earth and its atmosphere to space
24
Q
Which things effect daily temperature?
A
- Latitude
- Seasons
- Strong winds
- Wind direction
- Cloud cover
- Coastal or inland
- Surface type
25
Heat transfer methods? How do they work?
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
26
Earth heating processes? In/Out
Heat enters and leaves the earth/atmopshere via solar and terrestrial radiation respectively
Heat is then transferred within the atmosphere by conduction, convection, advection
27
What does the term albedo describe?
| Define Specific Heat
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
28
Seasons are based on what?
```
Average temperature (Not on position of earth relative to sun)
Due to lag of balance between incoming and outgoing energy
```
29
Four different types of inversions?
Radiation, Turbulence, Subsidence, Frontal
30
How does a radiation inversion form?
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
31
How does a turbulence inversion form?
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
32
How does a subsidence inversion form?
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
33
How does a frontal inversion form?
At any frontal surface where warm air is forced to rise over top of a layer of colder air
34
Effects of inversions on aviation?
```
Formation of cloud
Visibility
Turbulence
Dew Point
Wind shear present
Aircraft performance
```
35
Which gases are the primary heat absorbers in the atmopshere?
Ozone, Oxygen, Carbon Dioxide
36
Define atmospheric pressure
The total weight of the column of air above the point where the pressure is being measured
37
Define pressure lapse rate
Air pressure must always decrease with increasing height
| Approx 1hPa per 30ft
38
Define QNH
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
39
Define QNE
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
Define QFE
Aerodrome level pressure set on the altimeter
| When QFE is set, intrument will read height of the aircraft above aerodrome level
41
Define Transition Altitude and Level
Altitude 13000ft
Level FL150
Unusual to cruise between these altitudes
42
What is the effect of decreasing MSL pressure, when the sub-scale is not reset?
High-Low, Watch out below
| Will cause an altimeter under-reading
43
What are some causes of variations in pressure over distance or time?
Lee Trough
Thermal or Heat lows
Thunderstorms
Diurnal Variation
44
Three factors that contribute to high DA environments
Temperatures warmer than ISA
Pressures lower than ISA
High water vapour content
45
Effect of High DA on aircraft performance?
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
What type of general weather pattern would give negative pressure altitudes?
Temps lower than ISA
Pressures higher than ISA
Generally at lower airfields
47
Define DA
Pressure altitude corrected for non-standard (ISA) temperature variations
48
What is the rate of change of change of pressure?
30 feet per hPa
49
What is the standard surface wind?
Ten minute average of speed and direction, measured at 10m above the surface
50
What can SIGMETs be issued for?
```
Thunderstorms
Tropical Cyclone
Severe Turbulence
Severe Icing
Severe Mountain Waves
Heavy Sandstorm or dust storms
Volcanic ash cloud and volcanic ejecta
```
51
What do the following mean? INTSF, WKN, NC
Intensifying, Weakening, No Change in intensity
52
```
Define Cloud Amounts
SKC
NSC
FEW
SCT
BKN
OVC
```
NCD
```
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
Define Squall
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
Define Gale
A 10 minute mean wind speed between 34-47kts
55
Define Gust
Short term increase in wind speed lasting only a few seconds, must be greater than 10kts to be reported
56
How do you estimate surface wind from the air?
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
What are the 3 forces on acting to create wind at ground level?
1. Pressure Gradient Force
2. Coriolis Force
3. Friction
58
What causes coriolis force?
The inertial force that acts on objects that are in motion relative to a rotating frame of reference
59
What are 3 properties of the coriolis force?
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
Draw the geostrophic wind balance created in the southern hemisphere
PGF, CF and Friction force diagram
61
How does friction affect surface wind velocity? Diagram
Diagram with friction, gives wind vector from high towards low pressure on angle
62
Define Buys Ballots Law
If you stand with your back to the wind in the southern hemisphere, the low pressure is on your right
63
Define windshear
A sudden change in wind speed and/or direction over a short distance, either horizontally or vertically
64
What are the four categories of low-level turbulence?
1. Surface friction
2. Thunderstorms
3. Temperature Inversions
4. Frontal Activity
65
What are the causal factors of turbulence?
1. Convective
2. Mechanical
3. Wake Turbulence
4. Clear Air Turbulence
66
When would you expect wind shear associated with frontal activity?
When the temperature difference is greater than 5° across the front
OR
If the front is moving at more than 30 kts
67
What do you need for a katabatic wind to form?
| What is the NZ one called?
Clear nights
Sloping ground
Pressure gradient not too strong
- Greymouth Barber
68
What do you need for a katabatic wind to form?
| What is the NZ one called?
Clear nights
Sloping ground
Pressure gradient not too strong
- Greymouth Barber
69
What are favourable conditions for a sea breeze to form?
| Probably be able to describe too
A coastal situation (sea or lake)
Fine weather, especially summer time
Slack pressure gradient
The period mid-morning to late afternoon for onset
70
What factors enhance terrain channeling?
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
Define dew point
The temperature at which a parcel of air must be cooled at constant pressure to become saturated
72
Which processes take heat energy from the environment? (stored as latent heat)
Sublimation
Melting
Evaporation
73
Which processes release latent heat to the atmosphere?
Deposition
Freezing
Condensation
74
Why is relative humidity not useful as a measure of water vapour content?
When the RH changes, can't be sure if its due to amount of water vapour or a change in temp
75
Define Stable Air
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
Define Unstable Air
Air displaced vertically will become warmer than the environment (and therefore lighter) and will continue to rise when the lifting force ceases
77
Define Conditionally Unstable Air
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
Outline the adiabatic process
Parcel is forced to rise
Parcel subjected to less pressure
Therefore it expands
Expansion results in cooling
79
What are the values of DALR and SALR
```
DALR = 3° per 1000' (When RH is between 0-99%)
SALR = 1.5° per 1000' (When RH is 100% - Cloud)
```
80
If ELR < SALR ?
If SALR < ELR < DALR?
If DALR < ELR?
Air is stable
Air is conditionally unstable
Air is unstable
81
Which 4 factors cause air to rise in the atmosphere?
Convection
Orographic Lifting
Widespread Ascent (Low pressure or frontal system)
Turbulence
82
What weather conditions would be associated with cold southerly maritime flow?
```
Unstable conditions
Cumuliform cloud (Cu, TCu, Cb)
Showers of rain, hail, snow intermingled with patches of clear air
```
83
What weather conditions would be associated with warm northerly maritime flow?
Stable conditions
Stratiform clouds (St, Sc, Ns, As)
Drizzle and/or rain
84
```
What do the following terms mean?
Cumulus
Stratus
Alto
Nimbo
Cirrus
```
```
Cumulus - Pile (Heaped or puffy)
Stratus - Layer (Sheet-like)
Alto - Middle
Nimbo - Heavy rain
Cirrus - Curl (Streaky)
```
85
List the ten basic cloud types
Ci, Cc, Cs
Ac, As, Ns,
Cb, Cu, Sc, St
86
State the approximate cloud heights
High - 20,000' to tropopause
Middle - 6,500' to 20,000'
Low - Surface to 6,500'
87
What are the limitations of a ceilometer?
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
Be able to identify TCu and Cb
TCu - middle cloud, with absence of heavy rain
| Cb - Heavy rain, anvil head
89
How do you work out cloud base for convective and non-convective clouds?
Convective (TCu & Cb) Cloud base = 400x(Tsurface temp- Tdew point)
Forced lifting = 250x(Tsurface temp- Tdew point)
90
What are three processes that lead to cloud disspation?
1. Sinking of air
2. Mixing with clear air
3. Direct warming
91
Define the precipitation rates of light, moderate, heavy
Light - Between a trace of rain and <2.5mm/hr
Moderate - >2.5mm/hr and < 10mm/hr
Heavy - >10mm/hr
92
Describe the limitations of a forward scatter meter
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
What is the effect of light/moderate/heavy precipitation on visibility?
Light - Little reduction
Moderate - 3000m - 10km
Heavy - less than 3000m
94
What is the effect of fog and mist on visibility?
Fog <1000m
Mist >1000m
Haze < 5000m (Due to particles in air not water vapour)
95
What are the requirements for radiation fog?
```
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
```
