Met Flashcards
1
Q
At what distance is visibility measured in km instead of m?
A
More then 5000m
2
Q
Describe the composition of the atmosphere.
A
Nitrogen 78.09% Oxygen 20.95% Argon 00.93% Carbon Dioxide 00.03%
3
Q
What are the layers of the atmosphere from highest to lowest?
A
Ionosphere Mesosphere Stratosphere Troposphere
4
Q
What are the depths of the troposphere?
A
52,000ft/16km at the equator 36,000ft/11km at 50degrees north 30,000ft/9km at the poles
5
Q
Describe the conditions of the stratosphere
A
Extends from the troposphere to 50km with a constant temp of 0 degrees Celsius
6
Q
What is the difference between official and unofficial met observations?
A
Official is provided by a appropriately trained person at a unit with the necessary equipment. Otherwise unofficial.
7
Q
What are the conditions of the ISA?
A
International standard atmosphere .pressure of 1013.25hPa .air density 1225gm/m3 .temperature +15degrees Celsius . 1.98 degrees per 1000ft lapse rate
8
Q
What is insolation?
A
The incoming radiation from the sun warming the earth, as the air does not absorb the energy.
9
Q
What is specific heat capacity?
A
The energy required to heat 1kg of a substance by 1degree Celsius.
10
Q
What factors affect diurnal variation?
A
Surface- variation is greater over land and sea. Wind speed- wind causes turbulence that spreads the cooling effect through a greater depth of air. Cloud- reduces heat loss.
11
Q
How do inversions and isothermal layers affect the lapse rate?
A
Inversions cause the effect to reverse and the air actually heats up as it rises. Isothermal layers are where the temperature remains the same in that layer and doesn’t lapse.
12
Q
Define latent heat.
A
The heat required to cause a change of state, the actual temperature does not change during the change of state as the energy is used to actually change the state.
13
Q
How does the temperature of the air affect its humidity/saturation? What is the point at which a piece of air that is cooling becomes fully saturated?
A
Warmer air holds more moisture so as a parcel of air warms its ability to retain water increases so it is less saturated. The dew point.
14
Q
What is condensation?
A
When the parcel of air passes its dew point when cooling and the water vapour in it returns to liquid form.
15
Q
What four ways may a parcel of air be cooled past its dew point?
A
Conduction Evaporation Mixing Adiabatic cooling.
16
Q
Define adiabatic
A
The change in temperature of a parcel of air as its density changes, normally cooling as the air expands when rising.
17
Q
What are the adiabatic lapse rates for dry and saturated air?
A
SALR= 1.5 degrees/ 1000ft DALR= 3.0 degrees/1000ft
18
Q
What is the ELR?
A
The environmental adiabatic lapse rate that exists within the atmosphere at a particular time. (ISA global average is 1.98 degrees per 1000ft)
19
Q
Define stable and unstable air.
A
Stable air is air that doesn’t rise and unstable rises.
20
Q
What is absolute stability?
A
When the ELR is less than both the DALR and SALR creating stable air.
21
Q
What is conditional instability?
A
When the ELR lies between the SALR and DALR so dry air will be stable as it is cooler than the environment but saturated air will rise as it would be warmer.
22
Q
What is absolute instability?
A
When the ELR is greater than both the SALR and DALR meaning that both dry and saturated air will be unstable.
23
Q
What is the vertical distance associated with 1hPa change in pressure?
A
30ft
24
Q
How many inches of mercury are there in 1013.25hPa?
A
29.92
25
What does an altimeter set to QNH read?
The altitude, i.e. Vertical distance between you and MSL
26
What does an altimeter set to QFE read?
The height above a specified datum, normally aerodrome elevation.
27
What is the SPS and what does it give you?
The standard pressure setting of 1013.25hPa and it gives you your vertical position expressed as a flight level.
28
What is a RPS?
A regional pressure setting, same as QNH but covers a region. Used by aircraft below 3000ft outside CAS. Lowest forecast QNH in the region.
29
Define transition altitude.
The altitude at or below which the vertical position of an aircraft is controlled by reference to altitude.
30
Define transition level.
The lowest flight level available for use above the transition altitude.
31
Define transition layer.
The airspace between the transition altitude and transition level.
32
What is the fundamental process that causes clouds to form?
Condensation, caused by the air being cooled past its dew point either by; Adiabatic cooling through air rising Heat loss by conduction Temperature drop as a result of mixing (e.g. Turbulence)
33
What processes can cause air to rise and therefore cool?
Convection currents due to localised surface heating Frontal activity between adjacent air masses of differing temps (aka mass ascent) Orographic ascent cause by terrain Turbulent motion over undulating ground
34
Describe the convection current method of cloud formation.
Insolation causes the earth to heat up and this energy is then reradiated out into the air causing the air closest to the ground to warm first. This air then rises until it hits its dew point at which point it condenses into cloud. The extent of the cloud is dependent on the humidity and the strength of the rising currents.
35
Describe the frontal activity method of cloud formation.
When a mass of air of one temperature encounters one at a different temperature the warmer air will be forced upwards and cooled adiabatically until it hits the dew point and condenses.
36
What is orographic ascent?
An air mass forced to rise by the terrain rising, this causes the air to cool adiabatically until its dew point is reached. If the air is stable the cloud will only form in the vicinity of the hill or mountain as the air will warm again on its descent down the other side.
37
Describe turbulent mixing with regards to cloud formation.
Air mass moving quickly over undulating ground has its lower levels of air retarded by friction with the ground or obstacles causing turbulence which can form low clouds. Not normally much vertical growth.
38
What are the four cloud families?
High level- above 20,000ft Medium level- above 6,500ft Low level- below 6,500ft Clouds of vertical extent- those which extend over multiple levels.
39
What are the types of clouds?
Cirrus-wispy Cumulus- fluffy sheep Alto- medium Stratus- layers Nimbus- rain bearing
40
Define cloud base.
The height of the base of any cloud above the aerodrome elevation.
41
Define cloud ceiling.
The vertical distance from the elevation of the aerodrome to the lowest part of any cloud visible from the aerodrome which obscures more than one half of the sky.
42
What instruments are used to measure cloud base/ceiling and how do they work?
Ceilometer. Fires lasers up into the sky and measures the reflection.
43
What is used to assess cloud cover and what are the categories?
Oktas (eights of the sky) 0= NSC (no significant cloud) 1-2= FEW 3-4= SCT (scattered) 5-7= BKN (broken) 8= OVC (overcast)
44
What is precipitation and what are its dimensions?
Any moisture that is released from the atmosphere in either liquid or solid form. Water droplets- 0.02mm Drizzle- 0.2mm Heavy rain- max 5.5mm Hail- can reach larger diameters
45
Why is precipitation an important factor?
Supercooled water droplets- icing Wet surfaces- braking action Visibility- VFR/IFR Engines- flooding
46
What do you call water droplets that are below 0 degrees but have not frozen?
Supercooled
47
What do supercooled droplets need to freeze?
A freezing nuclei e.g. Particulates, aircraft skins, or already frozen droplets.
48
What are the types of precipitation?
Snow Sleet Drizzle Rain Hail
49
What are the four ways in which clouds can form?
Conventional Turbulence Orographic Frontal
50
Detail the different levels of intensity and durations of rainfall.
Intensity- light, moderate and heavy Duration- short, intermittent, or continuous
51
What types of precipitation are associated with stratus or stratocumulus clouds?
Drizzle, freezing drizzle or snow grains
52
What types of precipitation are associated with thick Altostratus and nimbostratus clouds?
Continuous rain or snow.
53
What types of precipitation are associated with thick Altostratus and stratocumulus clouds?
Intermittent rain or snow
54
What types of clouds can produce rain or snow showers?
Altocumulus, large cumulus and cumulonimbus
55
What types of cloud produce hard or soft hail?
Cumulonimbus
56
What three conditions must be present for a thunderstorm to develop?
Moist air Unstable air Trigger
57
What are the three stages of a storm cells development and briefly describe them.
1. Cumulus- growing stage, cloud grows very quickly following the trigger, strong vertical currents encourage growth, generally lasts 30 minutes. 2. Mature- raindrops and hailstones grow inside the cloud until the vertical currents can no longer hold them up, they then fall to the ground bringing cold air with them, the precipitation is heavy. This stage usually lasts 30 minutes. 3. Dissipating- precipitation gradually decreases, anvil shape forms as cloud growth stops, regeneration can occur if cloud joins with new cumulus clouds.
58
What are the hazards associated with thunderstorms?
Turbulence Hail Icing Lightning Static Windshear
59
What are the four classes of trigger action?
Air mass- e.g. Polar air being warmed by warmer land. Frontal- warm air pushed up by advancing cold front. Orographic Insolation- strong heating of land can lead to very unstable air.
60
What does icing depend on?
The size, shape and speed of the water droplets. Also the airframe must be 0 degrees unless the water droplets are supercooled.
61
Describe hoar frost.
Affects aircraft parked overnight, as the airframe cools by radiation water condenses on it and eventually freezes if cooling continues. This can happen on the ground or in the air if the cold airframe descends through warmer air.
62
Describe rime ice.
Rime ice occurs when supercooled water droplets hit the airframe and freeze almost completely. This produces a weak accumulation of ice that can affect aerodynamics and small air intakes.
63
Describe Clear ice.
Clear ice formed by water droplets that are only just supercooled so when they impact the airframe they do not freeze entirely and a large proportion of the drop flows backwards and freezes leading to heavy, thick ice. It can be dangerous even when it breaks off as it will do so in large chunks that can be hazardous to the aircraft.
64
Describe rain ice.
Most dangerous form, happens when water droplets that are only just supercooled hit an airframe which is 0 degrees leading to only a small proportion of the drop freezing and the rest flowing backwards and freezing rapidly. This creates a large wight penalty. This normally happens to aircraft flying into a cold front just ahead of a warm front.
65
List the types of icing in order of severity from least to most.
Hoar frost Rime ice Clear ice Rain ice
66
What parts of an aircraft does icing affect?
Wings and control surfaces Windscreens Propellers Radio antennas Tubes and vents Carburettors Jet engines
67
What type of cloud is normally associated with severe icing?
Cumulonimbus or even nimbostratus in certain conditions (thick heavy layers)
68
What is the difference between anti-icing and de-icing?
Anti icing prevents the build up of ice in the first place De-icing gets rid of ice that has already accumulated.
69
Give some examples of anti icing systems.
Systems that pump alcohol (what a waste), glycol or hot air over vulnerable surfaces. Electric heating elements Etc
70
Give an example of a de-icing system.
Rubber boots- those rubber things attached to wings that are inflated with compressed air and break the ice.
71
Define visibility
The ability, as determined by atmospheric conditions and expressed in units of distance, to see and identify prominent unlighted objects by day and prominent lighted objects by night.
72
Define fog and mist and what is the difference between the two?
Both are suspensions of small water droplets reducing visibility; To less than 1000m for fog 1000m or more for mist
73
What is haze?
A suspension of solid particles in the air which reduce visibility to not less than 1000m where the relative humidity is less than 95%
74
Describe radiation fog and what are the conditions required for it to happen?
Rapid cooling of the land on a clear night through radiation, this cools the layer of air closest to the ground causing it to reach its dew point and condense. Clear sky- allows earth to radiate heat and cool Land surface- to allow cooling of the air layer by conduction Moist air- so there is moisture to condense Light wind- between 2-8kts to prevent dispersal of air Long night- allows time for fog to form
75
Describe advection fog
A warm, moist mass of air being forced over a cold surface causing its temperature to drop and the air to condense. Wind speed not critical as air mass is moving anyway.
76
Under what conditions would smog form?
Normally under a temperature inversion causing the air to become stable and therefore preventing the dispersal of the pollutants.
77
What is the prevailing visibility?
The maximum value reached or exceeded in at least 50% of the circle around the aerodrome, the sectors of visibility do not need to be contiguous.
78
What is the minimum visibility?
The minimum value of visibility
79
Define RVR and how it can be measured.
The actual visibility along the runway as viewed from the perspective of the pilot in the cockpit. It can be measured by counting; -A series of marker boards along the side of the runway. -A series of lights of known intensity along the side of the runway. -or by a photo-optical measurement of atmospheric transparency along the runway.
80
When is an RVR reported?
When local visibility is less than 1500m
81
What are the conditions for CAVOK?
The visibility must be more than 10k (9999) No cloud below 5000ft or the minimum sector altitude (whichever is greater) No significant weather at the aerodrome No Cb or TCu
82
What type of north is the wind on anemometer given in?
Magnetic
83
What are Gusts and lulls?
Gusts are increases in wind speed and lulls are the opposite.
84
What is a gale?
Prolonged high speed wind with a mean value of 34kts or is gusting to 43kts or greater.
85
What is veering and backing in regards to wind velocity?
Veering is a clockwise change in wind direction. Backing is an anti-clockwise change in wind direction.
86
What is an isobar?
A line delineating areas of constant pressure. The closer they are the larger the pressure gradient.
87
Describe pressure gradient force.
The movement of air from an area of high pressure to low pressure. Creates wind.
88
What effect does the coreolis force have on wind in the northern hemisphere?
It deflects winds to the right, it does the opposite in the Southern Hemisphere. This is otherwise known as geostrophic wind
89
What is geostrophic wind?
The result of the Coriolis force acting on pressure gradient wind.
90
What is a cyclone?
Otherwise known as a depression, it is an anti clockwise rotation of air around an area of low pressure. Caused by the air flowing inwards to the low pressure area from all directions and deflecting to the right. Air converges from the surface and is forced upwards before dispersing, adiabatic cooling of this air will produce thick cloud and precipitation. These can lead to tropical cyclones.
91
What is an anticyclone?
A clockwise rotation of wind around an area of high pressure. Air converges and then descends to the surface before diverging. Creates stable and clear weather. In summer these create periods of fine settled weather. In winter radiation fogs.
92
Why does wind at the ground differ from higher winds?
Due to friction with the earth that slows it down, geostrophic force is also reduced. This means the wind will decrease and back to around one third of the geostrophic wind over land and two thirds over the sea.
93
What effect does heating and cooling have on surface wind?
Heating increases the turbulence which cancels out land irregularities and lessens the effect of friction, leading to the wind increasing and veering. Cooling has the opposite effect.
94
How do sea breezes form?
It is caused by the land heating up faster than the water and transferring the heat to the air above it which rises, cooler air from the sea then is pulled in to replace this air (advection). Geostrophic wind will cause the wind to veer meaning that the wind will not blow at right angles to the coast.
95
What is a land breeze?
The opposite of a sea breeze, the land cools faster than the sea and this causes a movement of air out to sea.
96
Describe katabatic wind
The air at the top of the mountain or hill cools quicker, becomes denser and sinks to the bottom of the mountain.
97
Describe anabatic wind
Insolation causes transfers heat to the air and this rises up the topography.
98
What is a fohn wind?
A wind down the leeward side of a mountain which is warmer than the windward side owing to the differences in temperature changes with the SALR and DALR. The air drops its moisture at the top of the mountain causing it to descend down the leeward side at DALR which warms it up quicker.
99
Describe mountain waves
Air that has travelled over an obstacle descends immediately and then rises again with lesser amplitude as if it were bouncing. This creates lenticular clouds and rotary clouds.
100
What is convection turbulence?
Insolation transfers heat to air near the surface which produces a convection current of varying strength.
101
What causes mechanical turbulence?
Large vertical variations at the ground level such as mountain ranges, it is also dependent on the strength of the surface wind, its stability and the nature of the surface.
102
What is the definition of wind shear?
A rapid change of wind speed and/or direction over a short distance horizontally or vertically. Can occur at any height. The situations most likely to cause wind shear are; - 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 the vicinity of standing waves -flying near, especially under, cbs
103
When must you report windshear?
Whenever it is reported to you, report it to landing and departing aircraft until you are certain or it has been confirmed that it no longer exists.
104
What should a windshear report contain?
A warning of the presence of it The height or height band where it was encountered The time at which it was encountered Details of the effect of the windshear on the aircraft.
105
What are microbursts?
Localised down drafts of short duration, high velocity winds.
106
What is clear air turbulence?
Turbulence that occurs without clouds indicating its presence. It can occur anywhere but is normally associated with the upper troposphere of lower stratosphere as well as jet streams. They will be experienced flying between the boundaries between warm and cold air. It can also be caused by standing waves.
107
What are the classifications of air masses?
Polar or tropical followed by continental or maritime.
108
What is associated with tropical maritime air masses?
Characteristics- high temps, high dew point, high humidity Modification- continuously cooled from below so often forms stratus clouds. Lower layers become stable Summer- warm, moist air and hazy with broken cloud over land. Advection fog over coasts and sea. Winter- warm and moist with low cloud or fog and drizzle.
109
What is associated with tropical continental air masses?
Characteristics- high temp, low dew point, low humidity. Modification- continuously cooled from below and humidity increased by evaporation over water. Usually remains dry enough to prevent cloud. Summer- warm and dry overland with little cloud but often hazy due to suspension of dust particles from air mass source.
110
What is associated with polar maritime?
Characteristics- low temperature, high dew point, high humidity Modification- heated from below and acquires moisture due to evaporation. Rapidly becomes unstable at lower levels permitting formation of large cumulus and cumulonimbus clouds with associated showers, gust winds and thunderstorms. Summer- cool with showers and possible thunder near the coast. Calm and clear inland. Good visibility except for precipitation. Winter- suffers surface over the cold land and becomes stable. Possible layer of cloud and fog overnight.
111
Polar continental, what is associated with this type of air mass?
Characteristics- low temp, low dew point, low humidity Modification- acquires moisture as it crosses the North Sea. May be sufficient to cause instability in lower layers. Winter- rain or snow showers but often cold and clear inland.
112
What is an Artic maritime air mass?
An artic maritime air mass has similar characteristics to a polar maritime air mass but is less moist and colder due to the shorter tracking across the sea. Uncommon during the summer but when it does occur it brings thunderstorms and unseasonably low temperatures.
113
In terms of pressure what is a ridge?
An are of high pressure which elongates to form a ridge of high pressure. Shown as a zig zag on charts.
114
What is a pressure trough?
An elongated area of low pressure marked on charts. All are associated increasing cloud and risk of precipitation.
115
What is faster, a cold or warm front?
A cold front
116
What are the characteristics of a warm front?
.Pressure falls steadily, remains steady as it passes .Wind may back and increases slightly before decreasing and backing agitating .Temperature and dew point rise .Ci CiS AS .Drizzle or light rain .Cloud base lowers .Poor visibility .May take hours to pass
117
What weather do you associate with a cold front?
.Wind beers and increases .Pressure falls and then rises. .Temperature and dew point fall. .Initially heavy precipitation but this peters off quickly. .take around an hour to pass. .Visibility generally better than it was. .Line squalls can form.
118
What are occluded fronts?
This happens when a cold front catches up to a warm front, the type of occlusion depends on the relative temperatures of the cold air on either side of the warm sector, cold front occlusion (cold front colder than the cold air in front of the warm front) warm front occlusion (the opposite).
119
Who is the met authority for the uk?
The CAA
120
Who provides the forecasting and climatological services in the uk?
The met office.
121
What are the met offices functions?
.Maintain a watch over meteorological conditions affecting rations within FIRs .Prepare sigmets and other information relating to its area of responsibility. .disseminate sigmet info
122
What are the types of reports which concern a FISO?
Metars, specis, TAFs, Aerodrome warnings
123
What is a METAR and what does it include?
A report of actual weather conditions at a particular aerodrome at a specified time. Includes; Surface wind Surface vis Any weather Cloud Air temp/ dew point QNH Remarks
124
What is a SPECI?
An amendment to a METAR that draws attention to an improvement or deterioration of a condition that might affect the aerodrome ops. Required following an accident.
125
What are the time periods for TAFS?
9, 24 or 30 hours, prepared every 3 hours.
126
What does NOSIG signify on a TAF?
That no significant change in met conditions is expected within the next two hours, otherwise a trend would have been recorded.
127
What sort of met conditions trigger an aerodrome warning?
Gales/strong winds Squalls Thunderstorm Hail Fog Frost/snow Freezing precipitation
128
What conditions trigger SIGMETS?
Thunderstorms Heavy hail Freezing precipitation Tropical cyclone Heavy sand/dust storm Volcanic ash Severe mountain waves Severe icing Severe turbulence
129
What is an ATIS?
A repetitive recording that is continuously transmitted on a VHF frequency, includes aerodrome status, current weather, ATIS info code.
130
What type of north is used to describe wind speed on a met report?
True
131
When is directional variation included on a met report?
If greater than 3kts and 60 degrees or more.
132
What does VRB mean on a met report?
Variable wind direction.
133
What does 0000 signify on a met report in regards to vis?
Vis less than 50m
134
When is vis variation reported?
When it is less than 1500m in one direction and greater than 5000m in another.
135
How is RVR denoted on a met report?
R followed by the runway and measured vis distance. Distance in metres measured from 50m to 1500m Letter P before distance means that it is higher than can be assessed. Letter M before distance means that it is lower than can be assesses. Mean values, U for trend improving D for opposite and N for no trend .
136
What types of clouds are notified on a met report?
Cumulonimbus and towering cumulus.
137
What does prob mean on a TAF?
Likelihood of proceeding change happening, 30 unlikely, 40 likely.
138
What validity periods can TAFs have?
9, 24 or 30
139
How often are TAFs issued?
Every 3 hours for 9 hour TAFs Every 6 hours for 24 and 30 hour ones
140
When are METARs issued?
Every 30 minutes at 20 past the hour and 10 to.
