Meteorology Flashcards
1
Q
What are the 5 layers of the atmosphere?
A
Exosphere (650km-10000km)
Thermosphere (85km-650km)
Mesosphere (50km-85km)
Stratosphere (7km-50km)
Troposphere (Earths surface to 7km)
N.B. Starting from outermost layer
2
Q
Where in the atmosphere does almost all weather phenomena take place and why?
A
In the troposphere because it contains virtually all atmospheric water vapour
3
Q
What are the qualities of troposphere?
A
- Marked fall of density, pressure and temperature with height
- Contains virtually all atmospheric water vapour from which clouds and most atmospheric weather phenomena are derived
- A marked variation in space and time in vertical and horizontal motion
- Temperature varies between 15°C and -55°C
- Extends from Earths surface up to about 7km
4
Q
What is the boundary between the troposphere and stratosphere called?
A
Tropopause
N.B. Temperature inversion between the troposphere and stratosphere. This makes exchange of air between these layers virtually impossible
5
Q
What are the qualities of the stratosphere?
A
- Contains biggest concentration of ozone
- Air is extremely dry
- Temperature increases with height and varies between -51°C and -15°C
- Extends from just above the troposphere to as high as 50km
6
Q
What are the qualities of the mesosphere?
A
- No heat source. Temperature decreases to the minimum found in the atmosphere. Between -80°C and -100°C
- Extends from about 50km to 85km
7
Q
What are the qualities of the thermosphere?
A
- Very high increase in temperature which can reach 1200 °C to 1700°C
- Many molecules and atoms are ionised due to bombardment of this region with high energy radiation from the sun - Ionosphere
- Extends from around 85km to 500-650km
8
Q
What is the composition of the atmosphere?
A
Constituents of Dry Air
78% Nitrogen
21% Oxygen
1% Argon, hydrogen and helium
Constituents of varying presence
1-4% Water vapour
~0.03% Carbon Dioxide
9
Q
What is the average temperature lapse rate?
A
1.98°C / 1000ft
N.B. Rate at which temperature decreases with height
10
Q
What is the formula for pressure?
A
Pressure = Depth x Density
11
Q
What can density vary according to?
A
Air temperature and water content
12
Q
What does pressure generally decrease with?
A
Height
N.B. Largest and most constant pressure change (with height). Also varies from place to place, temperature and water vapour content
13
Q
What is the average pressure at mean sea level?
A
1013.25hPa
N.B. International standard atmosphere
14
Q
What is the rate of decrease in pressure with increasing height?
A
1 hPa/30ft from Mean Sea Level (MSL) up to 20000ft
N.B. 1 hPa per 50ft at 20000ft and above and 1 hPa per 100ft at 40000ft and above
15
Q
What is density?
A
Mass per unit volume (1 cubic metre)
N.B. Therefore a specific volume of air with high density has a greater mass than the same volume of air with a lower density. Decreases with an increase in height
16
Q
What does density have an effect on in ATS?
A
- TKOF performance associated with runway length
- Lift of an aircraft and its rate of climb and ceiling
- Manoeuvrability of an ACFT due to aerodynamic forces created by control surfaces
- Amount of drag acting on an aircraft
- Power delivered by a jet engine due to oxygen content of air intake
- Thrust of propellers due to aerodynamic forces created by their blades
- Content of oxygen and as a consequence the human ability to survive at higher levels without appropriate cabin pressurisation
17
Q
What are tools used to gather MET data?
A
- Thermometers
- Radar systems
- Barometers
- Rain gauges
- Wind vanes / anenometers
- Transmissometers (RVR)
- Hygrometers (moisture)
- Satellites
18
Q
What are the units of atmospheric pressure?
A
- Hectopascals (hPa) or millibars (mb) - these are same value
- Inches of mercury (ins)
19
Q
What errors does a mercury barometer suffer from?
A
- Index error
- Temperature error
- Gravity error
20
Q
What is an aneroid barometer?
A
Measures pressure. Aneroid means without liquid and utilises a partially evacuated metal capsule that reacts to changes in air pressure by either expanding or contracting
N.B. Gradually replacing mercury barometers
21
Q
What errors do an aneroid barometer suffer from?
A
Index error
N.B. Correction chart is provided
22
Q
What is ISA, its values and the reason it is used?
A
International Standard Atmosphere
Assumed to be a perfect dry gas with constant composition at all levels
At Mean Sea Level
Temperature = +15°C
Pressure = 1013.25 hPa (29.92 ins)
Density = 1.225 kg/m^3
Above Mean Sea Level
Lapse rate is considered to be…
1.98°C/1000ft from MSL to 11km
0°C/1000ft from 11km to 20km
N.B. Used for calibration of altimeters and other instruments to avoid constantly updating/correcting instrument input to account for pressure and temperature variations
23
Q
What is the specific heat capacity of a substance?
A
The heat required to raise the temperature of 1kg of the substance through 1°C
N.B. Not a constant and varies with water needing 5 times as much heat as soil. Land will heat up much more during the day than the sea. Land also cools more at night than the sea
24
Q
How much of the suns energy reaches the Earths surface?
A
About half
N.B. This is because much of it is absorbed by water vapour and ozone, scattered by solid particles suspended in the air or reflected by cloud, ice or snow as it enters the atmosphere
25
What is insolation?
**Incoming solar radiation - the process that heats the Earth**
N.B. This is at too high a frequency to be absorbed by the atmosphere which is heated by the lower frequency energy emitted by the Earth (terrestrial radiation)
26
What are the three main ways heat is transferred?
- Radiation
- Conduction
- Convection
27
What is radiation?
**Transfer of heat between bodies that are not in contact, without heating the intervening space**
N.B. How the Sun heats the Earth
28
What is conduction?
**Transfer of heat between bodies in contact with each other but without movement**
N.B. This is how the ground transfers heat to the air in contact with it (terrestrial radiation)
29
What is convection?
**Transfer of heat by vertical movement**
N.B. This is how heat is transferred within the atmosphere, not by conduction, because air is a very poor conductor of heat
30
What factors does diurnal variation in temperature depend on?
- Surface - Greater over land than sea
- Windspeed - Wind causes turbulence that spread the cooling effect of the Earth through a greater depth of air
- Cloud - Reduces heat loss
31
What is meant by the temperature lapse rate?
**The rate at which temperature decreases with height**
N.B. Temperature normally decreases with height throughout the troposphere
32
What is an isothermal layer?
When temperature remains the same with height
33
What does a thermometer measure?
**Temperature**
N.B. Mercury thermometer is used. Reservoir of mercury at its base which expands and contracts with changes in temperature
34
What are the boiling points and freezing points of water? (Celsius, Kelvin and Fahrenheit)
**Celsius scale**
Freezing point H20 = 0°C
Boiling point H20 = 100°C
**Kelvin scale**
Theoretical absolute zero = 0°K (-273°C)
Freezing point H20 = 273°K
Boiling point H20 = 373°K
**Fahrenheit scale**
Freezing point H20 = 32°F
Boiling point h20 = 212°F
35
What is the formula to convert Celsius to Fahrenheit?
°F = 9 x (?°C)/5 +32
36
What is the formula to convert Fahrenheit to Celsius?
°C = 5 x (?°F - 32) / 9
37
What happens when water in the atmosphere changes state?
**Latent heat is either locked in or given back to the atmosphere**
N.B. For examples, when water evaporates, it takes energy from its surroundings and thus cooling it. When it condenses, energy is released and warms the environment. These exchanges influence climate
38
How is water present in the atmosphere?
**Solid
Liquid
Vapour**
N.B. Majority of weather is produced when water changes from one state to another
39
What is the process by which clouds are formed?
**Condensation**
N.B. If saturated air is cooled, water vapour content becomes too great and visible droplets will appear
N.B.B. A change of state has occurred, latent heat is released, causing atmospheric warming
40
What is sublimation?
The process where ice and snow (Solid) changes directly into water vapour (gas) without moving through the liquid stage
41
What is deposition?
The process where water vapour (gas) changes directly into ice (solid) without moving through the liquid stage
42
What limits the amount of water vapour present in the atmosphere?
**Temperature**
N.B. The higher the temperature, the more water vapour the air can hold in suspension and the density decreases
43
What is latent heat?
**The heat required to cause a change in state without a change in temperature**
N.B. Heat is hidden until change in state is reversed
44
What is relative humidity?
**Measurement of water vapour present in the air, expressed as a percentage, relative to how much would be required to cause saturation at that temperature**
N.B. Increasing temperature leads to a decrease in relative humidity and vice versa (such as when temperatures are higher in the day and lower at night)
45
What is dew point?
The temperature at which the air becomes fully saturated and can no longer hold any more water
46
Where do the majority of civil flights take place?
Troposphere
47
What is a temperature inversion?
When temperature increases with height
48
What is heat a form of?
Energy
49
What process is responsible for cloud, mist and fog formation?
Condensation
50
What is released when condensation occurs?
**Latent heat**
N.B. This is the principal power source behind most weather phenomena
51
__________ is an important factor in the performance of aircraft
Temperature
52
At a given pressure, what does high temperature imply?
**Low air density**
N.B. This has an adverse effect on both piston and jet aircraft
53
How is the atmosphere heated?
Terrestrial radiation
54
If air is cooled at constant pressure until it is holding its maximum quantity of water vapour, what is the air said to be?
**Saturated**
N.B. The temperature at which this occurs is known as the dew point
55
What instrument is used to measure relative humidity?
**Hygrometer**
N.B. There are 2 types. A hair hygrometer (human hair) and wet/dry bulb hygrometer (Stevenson Screen used at aerodromes)
N.B.B. The difference between dry and wet bulb temperatures enable the dew point to be calculated
56
What is adiabatic cooling?
- As air temperature increases, density decreases. If this air is surrounded by colder and therefore denser air, it will tend to rise.
- Pressure decreases with height so the rising air will expand and cool
57
What is the lapse rate?
The change of temperature with height. There are 3 lapse rates of significance:
- Dry Adiabatic Lapse Rate (DALR) = 3°C/1000ft (Unsaturated air)
- Saturated Adiabatic Lapse Rate (SALR) = between 1.5°C and 2°C/1000ft - Always less than the DALR because of the release of latent heat
- Environmental Adiabatic Lapse Rate (ELR) - localised lapse rate at any given time or location. Normally less than the DALR - can be measured by radiosonde balloon or satellites
58
What is DALR?
Dry Adiabatic Lapse Rate
3°C per 1000ft
59
What is SALR?
Saturated Adiabatic Lapse Rate
Between 1.5°C and 2°C per 1000ft
60
What is ELR?
**Environmental Lapse Rate - The rate at which air cools with height at a given time and location**
N.B. Average is 1.98°C per 1000ft
61
Define stable in relation to the atmosphere
A state in which any small perturbation to a body, or bubble of air, will encounter a restoring force which tends to return it to its original position
62
Define unstable in relation to the atmosphere
A state in which any small perturbation to an object encounters a force which will move the object farther from its original position
63
Define neutral stability in relation to the atmosphere
When perturbation to a body results in no restoring or displacing forced so that the body remains in its perturbed position
64
Air that is rising is said to be _________
Unstable
65
Air that is not rising is said to be __________
Stable
66
What is absolute stability?
When the ELR in a layer is less than the SALR
67
What is conditional stability?
When the ELR lies between the DALR and the SALR
68
What is absolute instability?
When the ELR is greater than both the SALR and the SALR
69
Other than adiabatic cooling, what other factors can cause air to rise?
- Frontal lifting
- Orographic lifting
- Convergence (depression)
- Convergence (thermal)
- Turbulence
70
What is frontal lifting?
- When cold air is replacing warm air, it tends to undercut it, because it is denser, which forces the warm air to rise
- When warm air is advancing, it tends to ride over the top of the cold air as it recedes
- Associated with unsettled weather
71
What is orographic lifting?
- Prominent geographical features such as
mountain ranges cause air to rise as it
attempts to pass over them
- Behaviour of the air when it reaches the top depends upon its stability
72
What is convergence (depression)?
- Where relatively low pressure exists at the surface of a depression, air will tend to move in from all directions to equalise the pressure.
- This accumulation of air is called convergence and it causes vertical movement within the atmosphere
- Causes turbulence
73
What is convergence (thermal)?
- As a surface is heated by the sun
it warms the air in contact with it.
- Heating of different types of surfaces causes an
unequal temperature rise, which, in turn,
produces local convection currents.
- As the air rises, the relative pressure at ground
level drops and air converges to equalise it
- Causes thermal turbulence
74
What is mechanical turbulence and the factors that affect it?
The result of friction between air and a rough surface
- Strength of the surface wind
- Stability of the air
- Nature of the ground
75
What factors does cloud formation depend on?
Humidity in combination with a drop in temperature needed for condensation to take place. A trigger action of some kind is needed to initiate the process
76
What is altimetry?
**The study of pressure variation within the atmosphere**
N.B. Pressure and density decrease with height
77
What factors affect air density?
- Pressure - the greater the pressure, the greater the density
- Humidity - the greater the humidity, the lower the density
- Temperature - the lower the temperature, the greater the density
78
What is the difference between QNH and QFE?
**QNH is pressure at mean sea level, QFE is pressure at the aerodromes elevation**
N.B. QNH will always be greater than QFE as pressure decreases with height
79
What is the transition altitude in the UK?
3000ft
80
What is a flight level (FL)?
A surface of constant air pressure, related to a specific pressure datum, 1013.25 hPa and is separated from other such surfaces by specific pressure intervals
81
What is QFE?
Pressure at level of an aerodrome. If this is set on the altimeter, it will indicate **height** above the QFE reference datum
82
What is QNH?
Pressure corrected to mean sea level (MSL) at a particular time, aerodrome or area. When set on the altimeter, it will indicate **altitude** above mean sea level
83
How are clouds dispersed?
Precipitation or evaporation
84
What is the cloud forming process?
- **Cloud is the presence of water droplets or ice crystals suspended in the atmosphere and forms when water vapour in the atmosphere condenses**
- **For condensation to occur, the air must be cooled below its dew point. This is achieved by one of the following processes:**
- Adiabatically by air rising and cooling
- Heat loss by conduction or evaporation
- Temperature drops as a result of mixing
85
What is the Bergeron process?
When ice crystals grow rapidly as water evaporates from water droplets and condenses or deposits onto the ice crystals. As they grow, they fall faster and sweep up more ice crystals and water droplets in the collision and coalescence process
86
What is supercooling?
**When temperature of water is lowered below 0°C without freezing**
N.B. Water droplets have much lower freezing point which gets lower with decreasing droplet size. It can be as low as -40°C
87
What are the triggers for cloud development?
- Free convection - Floats up in the atmosphere
- Slant-wise ascent - Frontal and orographic ascent
- Forced convection
- Turbulent mixing
88
Diurnal variation of clouds
Clouds formed by free convection have a very clear diurnal cycle as main triggering mechanism is surface heating by the sun.
N.B. Convective clouds forming in the morning indicated a conditionally unstable atmosphere
89
How are clouds classified?
Cumuliform (Heaped), Stratiform (Layered)
- Low cloud (Below 6500ft) - Stratocumulus (Sc), Stratus (St), Cumulus (Cu), cumulonimbus (Cb)
- Medium cloud (6500ft-20000ft) - Altocumulus (Ac), Altostratus (As), Nimbostratus (Ns)
- High cloud (20000ft+) - Cirrus (Ci), Cirrocumulus (Cc), Cirrostratus (Cs)
N.B. Refer to pictures and revision section of clouds slides
90
What sort of cloud is associated with unstable air?
Cumuliform
91
What type of cloud is normally associated with stable air?
Stratiform cloud
92
Define cloud base
The height of the base of any cloud above aerodrome level (of any amount)
93
Define cloud ceiling
Height of lowest clouds above aerodrome level covering more than half the sky
94
What is the cloud Okta scale?
Sky divided into 8ths
0 Oktas = Skyclear
1-2 Oktas = FEW
3-4 Oktas = SCT
5-7 Oktas = BKN
8 Oktas = OVS
95
Importance of cloud to ATS
- May reduce flight visibility, cloud ceiling can affect VFR flights
- Cloud type often indicates type of precipitation
- Icing may occur under certain conditions
- Large Cumuliform clouds indicate presence of significant turbulence
96
Significance of precipitation in ATS
- Reduces visibility and often appears in connection with low cloud.
- Heavy precipitation can be accompanied by downdraughts
- Snow or ice clearing
- Freezing rain
- Snow
- Ice
- Runway and taxiway contamination - reduced braking action
- Temporary closure of a runway or airport
97
How is weather reported in a METAR?
**Present weather = Precipitation, obscuration, other**
N.B. Qualifying descriptors e.g. Shallow (MI), Thunderstorm (TS), Shower (SH), Heavy (+), Light (-)
N.B.B. Can also be reported as recent or significant weather
98
What are the reportable types of precipitation?
- Drizzle (DZ) - Water droplets under 0.5mm
- Rain (RA) - Water droplets greater than 0.5mm. Heavy up to a maximum of 5.5mm
- Snow (SN) - Will reach ground is surface temp is 0°C or if 0°C temp level is low enough
- Snow Grains (SG) - Diameter generally less than 1mm (Frozen drizzle)
- Ice Pellets (PL) - Frozen rain drops/ melted refrozen snow flakes. 5mm less diameter
- Ice Crystals (IC) - Tiny unbranched ice needles
- Large Hail (GR) - Balls of ice diameter 5mm or more. Irregular shapes
- Small Hail (GS) - Hailstones less than 5mm
99
What type of rain do we get from clouds formed by slant-wise ascent?
Continuous rain
100
What type of rain falls from deep convective cloud?
Heavy showers of shorter duration
101
Define precipitation
Any moisture released from the atmosphere in either liquid or solid form
102
What size are water droplets in a cloud?
~0.02mm
103
How is intensity of rainfall categorised?
Light (-)
Moderate
Heavy (+)
104
How is duration of rainfall classified?
Short
Intermittent
Continuous
105
What cloud types are associated with drizzle, freezing drizzle or snow grains?
Stratus or stratocumulus
106
What cloud types are associated with continuous rain or snow?
Thick altostratus and nimbostratus
107
What sort of cloud is associated with intermittent rain or snow?
Thick altostratus and stratocumulus
108
What sort of cloud is associated with rain or snow showers?
Altocumulus, large cumulus and cumulonimbus
109
What sort of cloud is associated with hard or soft hail?
Cumulonimbus
110
When can ice form on the surface an airframe?
When the temperature of the airframe is below 0°C or if there are supercooled water droplets present
111
What does aircraft icing depend on and what are the main types?
Size and temperature of the water droplets involved as well as the shape and speed of the airframe
Rime ice
Clear ice
Hoar frost
Rain ice
112
When does rime ice occur?
- Tends to occur at very low temperatures less than -15°C
- Droplets freeze so rapidly on impact that they do not spread out
- Icing builds up, mainly on leading edges
- Air trapped between the droplets cause an opaque appearance
113
When does clear ice occur?
- Forms when larger super-cooled droplets hit the aircraft. Tends to occur between 0°C and -15°C
- The droplets tend to flow backwards, spreading out before freezing completely, some merging into each other
- Can build rapidly to heavy thick ice
114
When does rain ice occur?
- When rain falls through a layer where the temperature is below freezing. Normally the result of a temperature inversion.
- The most likely place for rain ice to occur for an aircraft is flying in cold air just ahead of a warm front
115
What parts of the aircraft can ice accretion affect?
- Wings and controls
- Windscreens
- Propellers
- Radio antennae’s
- Tubes and vents
- Carburettors
- Jet engines
116
Which 2 cloud types are particularly associated with severe icing?
- Cumulonimbus - Notably at levels where cloud temperature is between 0°C and -10°C
- Nimbostratus - Moderate to severe icing compounded by the length of exposure to the cloud
117
What kinds of ice occur on the ground?
- Hoar frost
- Frost
- Freezing fog (FZFG)
- Freezing rain (FZRA)
- Freezing drizzle (FZDZ)
N.B. All can affect braking action
118
When does hoar frost occur?
When a surface at sub-zero temperature comes into contact with moist air. Deposition occurs forming a white crystalline ice coating
119
What is cold soaked fuel frost?
Can form on upper and lower surfaces if the wings due to very cold fuel on board or from refuelling with fuel which is lower at a lower temperature than the outside
120
What are significant factors that affect aircraft icing?
- Temperature
- Water droplet size
- Airframe shape
- Kinetic heating
- Concentration
121
What is anti-icing and how is it achieved?
- Systems which inhibit ice formation such as pumping alcohol, glycol or hot air over vulnerable surfaces.
- Heating elements may also be fitted to discourage ice formation
122
What significant meteorological conditions are to be included in observations at aerodromes?
- Cumulonimbus
- Thunderstorm
- Moderate/severe turbulence
- Wind shear
- Hail
- Severe squall line
- Moderate/severe icing
- Freezing precipitation
- Severe mountain waves
- Sandstorm
- Dust storm
- Blowing snow
- Funnel cloud
N.B. Also included in AIRMET and SIGMET reports for en-route traffic
123
What can be reported as recent weather?
- Freezing precipitation
- Moderate or heavy precipitation including showers
- Moderate or heavy blowing snow
- Dust storm or sand storm
- Thunderstorm
- Funnel cloud (tornado or water spout)
- Volcanic ash
124
What is a thunderstorm?
- Storm which produces thunder and lightning.
- Occurs in well developed Cbs and indicate severe updrafts and downdrafts
125
What are the stages of thunderstorm development?
**Cumulus - Also known as the growing stage ~30mins**
**Mature - Lasts ~30mins**
- Microburst can occur
- Accompanied by heavy precipitation
**Dissipating stage - Can last more than 2 hours and regeneration may occur if joined with fresh cumulus cells**
126
What are the associated hazards of a thunderstorm?
- Turbulence
- Hail
- Icing
- Lightning
- Static
- Wind shear
- Microburst
127
How are thunderstorms classified?
By the source of their trigger action
- Air mass
- Frontal
- Orographic
- Insolation
128
What is a mesoscale system and examples of it?
Weather systems smaller than synoptic scales but larger than micro-scale and storm-scale cumulus systems
- Sea breezes
- Squall lines
- Mesoscale convective complexes
- Friction layer turbulence
129
Importance of visibility to ATS
- Virtually all flights depend on visual conditions at some stage
- VFR depends on visual contact with terrain and other ACFT during entire flight
- IFR depend on visual references on the ground and to a certain extent, during TKOF and landing stages
130
Visibility for aeronautical purposes is the greater of…
- The greatest safe distance at which a black object of suitable dimensions, situated near the ground, can be seen and recognised when observed against a bright background
- The greatest distance at which lights in the vicinity of 1000 candelas can be seen and identified against an unlit black background
131
What is RVR?
- Runway visual range
- Range over which the pilot of an ACFT on the centreline of a runway can see the runway surface markings or the line delineating the runway or identifying its centreline
- Normally measured when MET visibility falls below a certain level (generally 1500m) or RVR below 1500m
- Measured using human observer or transmissometers (IRVR)
132
How are obscurations sub-divided?
Hydrometeors (water based) and lithometeors (solid particles)
133
When must an obscuration be reported in the METAR?
When visibility is reported as 5000m or less
134
Examples of obscuration
Fog (FG) - Visibility less than 1000m
Mist (BR) - Visibility 1000m or more
Haze (HZ) - Same as mist but relative humidity below 95%
Smoke (FU)
Dust (DU)
Sand (SA)
Volcanic Ash (VA)
135
What is the difference between fog and cloud?
- The cooling required to produce condensation occurs differently
- The cooling required to produce fog or mist usually arises from radiation, advection or mixing
136
What is radiation fog and its requirements?
The result of cooling and condensation in the air near the ground. At night, the ground radiates heat and the air close to the ground loses heat by conduction.
**Requirements**
- Clear sky - Earth radiates heat energy
- Land surface - Rapidly cool and conduct this cooling to the adjacent air
- Moist air - Layer contacting ground will reach dew point
- Light wind - Between 2 and 8kts to provide right amount of turbulence
- Long night - Allows maximum time for effect to become established
137
How does wind speed affect radiation fog?
- No wind = Dew or shallow fog
- 2-8kts wind = Thin layers of fog
- >8kts wind = Turbulence lifts fog to form stratus clouds
138
How is advection fog formed?
- Warm, moist air moving over a colder surface can cool the air near the surface below its dew point
- Called sea fog when it forms over the sea
139
How is hill fog formed?
Air moving up slopes and condensing at the top, to form low cloud/hill fog
140
How is precipitation or frontal fog formed?
Can be formed if air becomes saturated during continuous rain preceding a warm front or warm occlusion
141
How is steam fog formed?
- Caused by cold, dry air moving over relatively warm moist water
- Small quantities of water evaporate into the air and cause localised condensation that resembles steam or a thin layer of thick fog at the water’s surface
142
Visibility is reported in the following intervals
THIS NEEDS CLARIFYING TOMORROW
THIS NEEDS CLARIFYING TOMORROW
143
Define prevailing visibility
The greatest visibility value reached within at least half the horizon circle or within at least half of the surface of the aerodrome
144
When is minimum visibility reported?
- When the lowest visibility is less than half the prevailing visibility or less than 1500m
- Reported along side prevailing visibility along with its general direction
145
How is sky obscured reported?
- VV///
- Reported in lieu of cloud information when sky is obscured due to fog, falling or blowing snow
146
What de-icing fluids in relation to aircraft?
- Fluids which are capable of removing ice and remain in place to prevent ice return for a set period of time
- This set time period is known as the hold over time (HOT) and is dependent on the quality of fluid used
- 4 types of deicing fluid - I, II, III, IV which increase with quality
147
What is a microburst?
A localized column of sinking air (downdraft) within a thunderstorm and is usually less than or equal to 2.5 miles in diameter
148
What are the IRVR requirements for each ILS/MLS category?
- CAT I (<2000m LDA) - TDZ IRVR recommended
- CAT II (<2000m LDA) - TDZ and MID IRVR required
- CAT II (>=2000m LDA) - TDZ and MID IRVR required, STP IRV recommended
- CAT III (All runways) TDZ, MID and STP IRVR required
149
What is a METAR?
Meteorological Aerodrome Report - made every 30 mins at 20 past and 10 to the hour
150
What is a landing forecast or trend type forecast?
A concise statement of the expected trend of the meteorological conditions at an aerodrome. Added to METAR and validity shall be 2 hours from time of the report
151
What is a TAF?
Terminal Aerodrome Forecast issued by MET office at a specified time and consist of a concise statement of expected MET conditions for a specified period of not less than 9 hours or not less than 24 hours
152
What do area and route forecasts contain?
Upper winds, upper air temperatures, significant en-route weather phenomena, associated clouds
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How is a SIGMET made up?
1. Location indicator or ATSU serving the FIR or ACC
2. Message identification and sequence number
3. Date and period of validity preferably not greater than 4 hours and certainly not greater than 6
4. Location indicator of the MET OFFICE originating the message
5. Name of the FIR or control area for which SIGMET is issued
6. Phenomena and description
7. Location of phenomena
8. Levels at which phenomena observed
9. Anticipated changes
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What instrument is used to measure wind and what are its units?
An anemometer and its direction is displayed in degrees magnetic and speed in knots
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What are units for wind in the METAR?
Degrees true
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Why is wind important in ATS?
- Major environmental factor affect ACFT movement in relation to the ground?
- Landing phase is critical for all flights and presence of wind shear is a major hazard as it can cause an aircraft to lose lift
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What is a Hadley cell?
When air at lower levels converges from both the northern and southern hemisphere into a region known as the Inter-Tropical-Convergence-Zone (ITCZ)
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What is wind?
**The horizontal movement of air over the surface of the Earth**
N.B. The movement of air from an area of relatively high pressure, to an area of relatively low pressure
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What is an isobar?
Continuous lines displayed on met charts joining places of equal pressure, normally at MSL
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What do closely spaced isobars mean?
**Strong winds**
N.B. Pressure gradient exerts force perpendicular to isobars and produces gradient wind
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What is Coriolis effect?
The rotation of the earth causes the air to spin
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Coriolis force prevents air from flowing directly from __________ pressure to __________pressure
1. High
2. Low
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What is a squall?
**An increase in wind that lasts for minutes**
N.B. Associated with active cumulonimbus clouds
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What is an increase in wind know as?
Gust
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What is a decrease in wind known as?
Lull
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What is a prolonged high speed wind that has a mean value of 34kts or is gusting to 43kts or later?
Gale
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What is Buys Ballots Law?
If you stand with your back to the wind, the low pressure lies to your left in the northern hemisphere
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GEOSTROPHIC WIND
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Weather: Clear and Sunny
Turbulence: __________
Friction: __________
Wind: __________
1. Turbulence increased
2. Friction decreased
3. Wind increases and veers
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Weather: Dull and cloudy/Night
Turbulence: __________
Friction: __________
Wind: __________
1. Turbulence decreased
2. Friction increased
3. Wind decreases and backs
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SEA BREEZE
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LAND BREEZE
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What is an anabatic wind?
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What is a katabatic wind?
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Valley winds
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What are mountain/standing waves?
**Air rises to cross and obstruction, descends immediately beyond it and then continues to rise and fall with gradual decreasing amplitude as the distance from the obstruction increases**
N.B. Strong vertical air currents and often indicated by presence of lenticular clouds. Roll clouds can also form downwind of the ridge and indicate maximum turbulence
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What is a föhn wind?
EDIT LATER
A warm dry air that blows down the leeward side of hills or mountains. Happens because of the difference in value between the DALR and SALR
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What is a thermal wind?
A wind that blows as a result of a difference in temperature between adjacent atmospheric areas
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What is a jet stream?
180
What is wind shear?
**A rapid change of wind speed and or direction over a short distance**
N.B. Can occur at any height but far more dangerous when encountered close to the ground
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What is convective turbulence?
Insolation on a sunny day heats the Earth and temperature rise is produced which varies according to each surfaces specific heat capacity. In conditions of light wind, there may be significant variations in convection currents and these affect ACFT at low level and speed. Characterised by smooth flight above cloud but bumpy below clouds
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What is mechanical turbulence?
SEE OTHER FLASH CARD
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Situations a pilot is likely to encounter wind shear
- Climbing or descending through an inversion
- Climbing or descending through a warm front
- In the lee of high ground or large buildings when close to the ground
- In vicinity of standing waves
- Flying near and especially underneath Cbs
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What is a microburst?
A localised column of sinking air (downdraft) within a thunderstorm and is usually less than or equal to 2.5 miles in diameter
*N.B. Low Level Wind Shear Alert System can warn of them
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What is a macroburst?
Basically a large microburst. More than 2.5 miles in diameter and produce winds as high as 135mph
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What is clear air turbulence?
EDIT LATER
Occurs without any cloud to indicate presence. Can occur anywhere in the atmosphere but normally associated with strong winds in the upper troposphere or lower stratosphere. Associated with jet streams
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What is an air mass?
A volume of air with many uniform characteristics extending over a large region
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How are air masses classified?
REWRITE LATER
- Arctic - Very cold and humid
- Polar maritime - Cold and humid
- Polar continental - Cold and try
- Tropical maritime - Warm and humid
- Tropical continental - Warm and dry
- Equatorial - Hot and humid
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Cold Air Over a Warmer Surface
- Stability: __________
- Type of clouds: __________
- Cloud base: __________
- Precipitation: __________
- Visibility: __________
- Stability: Unstable with convection
- Type of clouds: Convective
- Cloud base: __________
- Precipitation: __________
- Visibility: __________
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Warm Air OVer a cold surface
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What are depressions or cyclones examples of?
Low pressure systems
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What are anticyclones an example of?
High pressure system
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What are depressions characterised by?
- Strong winds and rising air leading to condensation, cloud development and precipitation
- Anti-clockwise in the northern hemisphere
- Typically 1000-2000km across extending from surface to tropopause
- Recognisable on a weather chart by pressure decreasing towards the centre of the system
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What are anti-cyclones characterised by?
- Opposite of cyclones/depressions
- Clockwise in the northern hemisphere
- Extend 2000-4000km horizontally and from surface to tropopause
- Central area of highest pressure is fairly large and isobars are widely spaced
- Light winds and subsiding air lead to clear skies and fine weather with no precipitation
- Fog or low clouds are not uncommon in anticyclones during winter due to low level inversions formed by air subsiding over a cold surface
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What is anticyclonic gloom?
196
What is a front?
A boundary between 2 air masses
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Warm front
Warm, moist, unstable air replacing cold dry and stable air. rides on top of a cold air mass - associated with stratus cloud and continuous rain.
Approaching warm front passing through are cirrus clouds, pressure falls steadily and temperature rises then cirrostratus, altostratus form and then nimbostratus providing continuous rain.
When passing, pressure remains steady or continues to fall slowly, wind decreases and veers, temperature and due point rise. Low nimbo/fractostratus persist but rain lightens to drizzle or ceases, poor visibility persists, may take several hours to pass
When receding, wind is light in warm sector, temperature, pressure and dew point remain steady, low stratus usually remains, mist or fog may persist
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Cold front
Cold dry stable air undercuts warm air and forces it up. Lots of convective activity - cumulus leading to TCUs and Cbs/thunderstorms
An approaching cold front, wind speed increases to moderate and pressure falls. Dew point and temperature generally remain steady and precipitation increases.
In a passing cold front, wind increases and veers, rapid pressure rise and temperature and dew point fall sharply. Heavy precipitation- thunderstorms/squalls. Takes around an hour to pass
Receding cold front - visibility very good, rain and cloud replaced by scattered cumulus, wind moderate and steady, pressure rising slowly. Temperature and dew point unchanged
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Occluded front
When a cold front catches up with a warm front. Associated with poor weather - embedded Cbs. Can be cold front occlusion Colder air on left than on right undercutting warm air or warm front occlusion where cold air on the left and colder on the right
200
What is a line squall?
201
Who is responsible for international standards in aviation?
The WMO (World Meteorological Organisation)
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What is WAFS?
World Area Forecast System - forecasts if global met parameter, upper wind and temperature information
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What is SADIS?
Satellite Distribution System - provides error free satellite data on vital flight information
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What is a MWO?
Meteorological Watch Office - Serves other met stations and offices within a designated area - normally an FIR
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What is an RAFC?
Regional Area Forecast Centre
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What is VAAC?
Volcanic Ash Advisory Centre
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Methods of met observation
Surface observations
Upper air observations
Observations from ACFT in flight
Observations from satellites
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What reports are available at aerodromes?
- METARs - Actual conditions at a specified time usually each hour or half hour. Surface wind and vis (including RVR), weather, cloud, temp/dew, QNH, remarks
- SPECIs - An amendment to a METAR showing improvement or deterioration of certain amounts
TAFs - forecast of expected MET conditions during a specified period - every 3 hours for 9 hour period, every 6 for 24/30 hour TAFs - trends added to METAR (ICAO not UK) for next 2 hours sig changes
- Aerodrome warnings - from MWO - Gales/strong wind warning, squall, thunderstorms, hail, fog, frost/snow, freezing precipitation in force fore validity period stated
- Wind shear warnings - based on recent pilot reports
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Low level wind shear alerting system (LLWSAS)
- Below 1600ft at some airports
- Mean surface wind speed at least 20kt
- Difference between mean surface wind and gradient wind at least 40kt
- Thunderstorm or heavy showers within 5nm of airport
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SIGMET
Subsonic flights
- Active thunderstorm
- Freezing rain
- Severe turbulence
- Severe mountain waves
- Tropical cyclone
- Heavy hail
- Severe icing
- Heavy dust/sandstorms
- Volcanic ash cloud
Transonic + supersonic flights
- Moderate or severe turbulence
- Cumulonimbus clouds
- Hail
- Volcanic ash cloud
Prepared by MET office and send to aircraft in flight up to 500nm on route or 2 hours flying time by ACC/FIC. Valid for 4 hours and reissued if necessary
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AIREP
Aircraft observations
- Severe turbulence or icing
- Severe mountain wave
- Thunderstorms with or without hail
- Volcanic ash or pre-eruption
- Any other phenomena that in the opinion of the pilot may adversely affect the safety of aircraft operations
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ATIS
Automatic Terminal Information Service
Transmits aerodrome status
Current weather
ATIS information code
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Meteorological bulletin headings
SA = Routine aerodrome report (Surface Actual)
SP = Selected special report
FT = Forecast valid for 18-24 hours
FC = Forecast valid for 9 or 12 hours
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What information is required by aerodrome and approach control on a routine basis?
- METAR with trend as appropriate, every hour or half hour
- SPECIs as appropriate
- TAFs
- Aerodrome warnings
- SIGMETs
- Additional info as agreed locally
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ATC will only transmit what has been supplied by the MET office but there are exceptions, what are these?
- Indicated wind speed and direction
- RVR obs
- Controller obs of sudden deterioration
- ACFT reports of weather hazards
- Cloud echoes observed on a radar
- Official MET observation (certificated)
- Unofficial MET observation
WILL BE ASKED IN AN ORAL BOARD
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VOLMET
Basically an ATIS on a loop for local aerodrome
