Meteorology Flashcards
What climate zone is the UK situated in?
Temperate
Characteristics of a temperate zone
Hot and warm summers, drier than other seasons
Where does the atmosphere extend further into space?
Around the equator
Two reasons for atmosphere being more extended at equator than poles?
Earth’s rotation
Greater heating at equator
Thickness of atmosphere is proportional to
Temperature
In ISA, what atltitude is the tropopause at?
30,000ft
Aircraft fly mostly in what atmosphere subdivision?
Troposphere
What lies between the Earth’s surface and the stratosphere?
Troposphere
The trophosphere’s relation to temperature?
Proportional
Temperature in the stratosphere is..?
Constant
Troposphere’s characteristics at the poles?
Colder and shallower
Approx. what temp is the stratosphere?
-57 degrees Celsius
What substance in the air is critical for life on earth?
Water Vapour
In ISA, temp decreases at what rate?
2 degrees celcius per 1000ft gained
Name of lines on pressure maps connecting areas of similar pressure
Isobars
Variation of pressure with horizontal distance is called…
Pressure gradient
Impact on aircraft performance on humid damp days is due to
Higher proportion of water molecules in air reduces overall air density
Regular pressure variations owing to daily heating and cooling effects of the sun is called
Semi-diurnal variation of pressure
What kind of barometer is used in aircraft altimeters?
Aneroid
Altimeter reading 0ft at sea level would read what altitude if the pressure drops 10hPa?
300ft
Sun’s radiation strikes polar regions at what kind of angle?
Oblique
Transfer of heat energy from one body to another is called..
Diabatic process
When heat is neither added or removed from a system, it is called..
Adiabatic process
Expansion and compression of gases experience what kind of heat process?
Adiabatic process
Relationship between temperature and radiation wavelength
The higher the temperature of the body, the shorter the wavelength of the radiation
Convection describes
Process by which warm air rises into the atmosphere and carries its heat energy with it
Why does warm air rise?
It is less dense than the surrounding air
Advection follows what other diabatic process?
Convection
Advection describes
Horizontal motion of air replacing air that has risen due to convection
What has a higher heat capacity? Water or land
Water
Because water has a higher heat capacity than land, land does what?
Heat and cool more quickly than water bodies
ELR stands for
Environmental Relapse Rate
What describes the process of temperature change from altitude increase in the real world?
ELR
What is the DALR?
Dry Adiabatic Lapse Rate
DALR equates to
3 degrees celcius reduction for each 1000ft climbed
If water vapour condenses in a discrete parcel of air, what will happen?
The parcel of air will cool at a lower rate
What is the SALR?
Saturated Adiabatic Lapse Rate
SALR occurs when?
Parcel of air cools at a lower rate than DALR due to water vapour condensing and latent energy being released
Stable atmosphere occurs when…
ELR is less than SALR and DALR
Stable atmosphere means air has what tendency?
To return back to its origianl position if displaced
Stable atmosphere’s typical weather
Clear skies, fog, stratus
Unstable atmosphere occurs when
ELR is greater than SALR and DALR
Unstable atmosphere means air has what tendency?
Rise if displaced
Unstable atmosphere’s typical weather
Cumulus and cumulonimbus cloud
Conditional instability occurs when
ELR is less than DALR but greater than SALR
Conditional instability means
Dry, unsaturated air is stable. Moist, saturated air is unstable
In what conditions do temperature inversions occur?
Low wind and clear nights
At night, cooling air not mixing with higher altitude warmer air results in…
Temperature inversion
Approximately what degrees is the Earth tilted at from the vertical?
23 degrees
Why does warm tropic air move towards higher latitudes?
The air cannot rise higher due to stratospheric isotherm
What generally happens to cool air over the poles?
It sinks
General circulation consists of how many main cells?
3
What is the equatorial trough?
A band of low pressure at the earth’s surface in the tropics
What is the process by which surface air will move towards an area of low pressure?
Convergence
What is the process by which surface air will move outwards from an area of high pressure?
Divergence
What temp is absolute zero?
-273 degrees celsius
The transfer of heat by the horizontal motion of an air mass is called?
Advection
The transfer of heat by the vertical motion of an air mass is called?
Convection
What is wind?
Horizontal flow of air across the Earth
Wind Velocity is the combination of what?
Wind direction and wind strength
A wind changing in a clockwise direction is doing what?
Veering
A wind changing in an anti-clockwise direction is doing what?
Backing
Wind caused by rotation of the Earth is called
Coriolis force
Geostrophic wind results from what…
Balance between coriolis force and pressure gradient force
Increasing latitude does what to the relative motion of earth
Reduces the easterly motion of the earth
The Earth’s rotation has what effect on the relationship between the Earth and a parcel of air
It will lag behind the easterly motion of the parcel of air
Observer’s experience of the coriolis force
Wind is deflected to the right
Coriolis effect increases with
Airflow
Coriolis effect cannot occur without
Airflow
Why is the Coriolis effect greater away from the equator?
Changes in latitude cause more significant changes in the difference of easterly movement
In the northern hemisphere, the Coriolis effect deflects the wind to the..
Right
Leftward deflection of wind by Coriolis effect occurs where?
Southern hemisphere
Geostrophic wind’s relationship to isobars
It flows parallel to the isobars
Best sentence to describe the formation of geostrophic wind
The pressure gradient force gets the air moving and the Coriolis effect turns it to the right
Geostrophic wind parallel to isobars has the low pressure on what side?
Left
Buys Ballot’s Law is…
Standing with your back to the wind in the northern hemisphere, the low pressure will be on your left
Flying from high to low pressure (in Northern Hemisphere) is indicated by what?
Right starboard drift, as the wind is from the left
Right starboard drift (in Northern Hemisphere) indicates what?
Flying from high to low pressure
Flying from low to high pressure (in Northern Hemisphere) is indicated by what?
Left drift
Left drift (In Northern Hemisphere) indicates what?
Flying from low to high pressure
In the NH, wind flows in what direction round a high?
Clockwise
In the NH, wind flows in what direction round a low?
Anti-clockwise
In the NH, wind flowing clockwise indicates a what?
High pressure
In the NH, wind flowing anti-clockwise indicates a what?
Low pressure
Wind blowing around a low experiences what process?
Pressure gradient force is greater than the Coriolis force
Wind blowing around a high experiences what process?
Coriolis force is greater than the pressure gradient force
Surface wind is usually measured at what height
30 ft
Why is wind usually less strong at the surface compared to higher levels?
Earth’s surface exerts friction
Friction causes surface wind to what?
Weaken in strength and back in direction
In general, the more unstable atmospheric stability is results in what effect to surface wind
It backs less and is more similar to the 2000ft wind
Why is windspeed greater around a high compared to an equally-spaced-isobar low?
Coriolis force increases with wind speed
Diurnal can be thought of as another word for..?
Daily
Roughly speaking, what altitude does the top of the boundary layer occur? (And frictional/thermodynamic effects become negligible)
2000 to 3000 feet
What part of the day does mixing of wind layers reduce?
Night
What happens to wind at night?
Slacks and backs
Why does sea breeze occur on sunny days?
Land heats more quickly than the sea
Light winds + convection near water =
Sea breeze
Vertical extent of a sea breeze is usually what?
1000 to 2000 feet
Why does sea breeze cause visibility problems?
It may bring cool, moist air over land
When does sea breeze occur?
Day
When does land breeze occur?
Night
Basics of a land breeze?
Land cools quicker than the sea, cooler land air replaces rising warm sea air
What kind of heat transfer causes air to cool during clear, cloudless nights?
Conduction (due to ground becoming cool because of terrestrial radiation)
In what land type does katabatic wind occur?
Mountainous
What causes katabatic wind?
At night, cool air flows down mountain slopes creating wind blowing into valleys
What two kinds of wind occur exclusively in mountains/hills?
Katabatic and Anabatic
What causes anabatic wind?
Warm air rises up a mountain slope
Why is anabatic wind weaker than katabatic wind?
Air flowing upwards is opposed by gravity
Cumulonimbus clouds’s up/downdraughts can extend how far into clear air around them?
20nm
High pressure systems do what to temp inversions?
Detach them from the surface
What cloud formation occurs in the lower lee side of a mountain during mountain wave?
Rotor cloud
In the tropics, pressure gradients are usually…
Weak
Why is the Coriolis force very weak in the tropics?
The distance of isobars from the earth’s axis remains constant
What wind system dominates in the tropics?
Pressure gradient force
What are used instead of isobars in the tropic systems?
Streamlines and isotachs
What do streamlines indicate?
Wind direction
What do isotachs indicate?
Areas of equal wind strength
Outdraughts in a tropic area come from where?
High pressure areas
Indraughts in a tropic area come from where?
Low pressure areas
What do vertical gusts do to an aircraft’s performance?
Increase its angle of atttack
During turbulence, why is it good practice to hold the attitude, not the altitude?
Avoid using the elevator excessively to not over-stress the airframe
Mountain wave occurs during what system?
High pressure
ATC wind reports are relative to..?
Magentic north at the airfield
Metereological reports on wind direction use what relative indication?
True North
A parcel of air moving in line with the pressure gradient force will experience Coriolis acting at what angle to its motion?
Perpendicular
Wind that flows around curved isobars is called the..?
Gradient wind
In the northern hemisphere, the mean surface wind direction compared to the gradient wind direction will…
Back
In what pressure system is vertical motion more upward?
Low pressure because the atmosphere is unstable
Lenticular cloud is a good indication of..?
Mountain wave and severe turbulence
What are the four forms of cloud?
Cirriform
Cumuliform
Stratiform
Nimbus
High-level cloud has what minimum base?
20,000 feet
Why does high-level cloud look fine and spideery?
Usually formed in coldest region of troposphere asice crystals rather than water particles
Description of cirriform
Fibrous
Description of cumuliform
Heaped
Description of stratiform
Layered
Description of nimbus
Rain-bearing
Clouds: cirru/cirro denotes what kind of cloud?
High-level
Stratus means what?
Layer
Cirrus means what?
High
Middle-level cloud occurs in what altitude range?
6,500ft to 20,000ft AMSL
What is virga?
Rain that does not reach the ground
Virga occurs in what kind of air?
Dry or warm air
Why does virga not reach the ground?
It evaporates or sublimes first
Alto- denotes what?
Middle-level cloud
Clouds: fractus denotes what?
Stratus or cumulus shreds below nimbo/alto-stratus
Clouds: castellanus is what?
Cumuliform clouds that are turret-shaped
Castellanus indicates what?
Unstable atmosphere
When water changes state, its transferred heat energy is known as..
Latent Heat
What does humidity measure?
The amount of water vapour present in the air
A saturated parcel of air means it has __% humidity?
100%
Relative Humidity Equation
RH = Vapour Pressure/Saturation Vapour Pressure
What factor determines how much water a particular parcel of air can support, regarding humidity?
Air temperature
Air temperature is proportional to how much water that air can support?
True
Relation between air temperature and saturation
The higher the air temperature, the more water it can support
How much water a parcel of air can support is formally known as?
Saturation Vapour Pressure
What is the Humidity Mixing Ratio?
Ratio of the mass of watter vapour in a parcel of air to the mass of dry air in the same parcel
What happens to the relative humidity of a rising unsaturated parcel of air?
It increases because temperature decreases and cooler air cannot hold as much water vapour
Why does rising unsaturated air increase in relative humidity?
Cooler air cannot hold as much water vapour
What remains constant in a rising parcel of unsaturated air?
Humidity Mixing Ratio
What is the dewpoint?
Temperature at which a parcel of air becomes saturated if it cools
What happens to a dewpoint related to moisture?
The moisture in the air, the higher its dewpoint temperature
What happens if a parcel of air is cooler than its dewpoint?
Excess wateer vapour will condense as water droplets
Two adiabatic ways in which cloud is formed
Mass uplift
Convection
Two diabatic ways in which cloud is formed
Advection
Radiation
What is the DALR?
3 degrees per 1000ft
Why is cooling not as great for saturated air as it continues to rise?
Latent heat is released due to condensation, so cooling is not as great
What is the SALR?
Saturated Adiabatic Lapse Rate
SALR’s relation to DALR?
Approximately half
Approximately, what rate is SALR?
1.5 degrees per 1000ft
What primary factor determines the type of cloud formed?
Stability of the atmosphere
What are the three kinds of atmopsheric stability when it comes to ELR/DALR/SALR and cloud formation?
Unstable, neutral and stable
ELR stuff: when does unstable air occur?
ELR is greater than DALR or SALR
ELR stuff: when does stable air occur?
ELR is less than DALR or SALR
ELR stuff: when does neutral air occur?
ELR is equal to DALR or SALR
In unstable air, clouds and air do what?
Continue to move verticaally after displacement
What clouds are typically formed in unstable air?
Cumuliform
What clouds are typically formed in neutral air?
Stratiform clouds
In neutral air, what happens to the air?
Remains in the position to which it was vertically displaced
In stable air, what happens to the air?
Returns to the position from which it was displaced
What clouds are typically formed in stable air?
Stratiform clouds or fog
When a parcel of air cools to the same temperature of its surrounding environment, it does what?
Stops rising
Air flowing over mountains cools and rises in what way?
Adiabatically
Why does cloud formed over mountains cease to exist as it descends on the lee side?
Temperature exceeds dewpoints and therefore water vapour vapourises
A cloud that forms as a ‘cap’ over the top of a mountain is known as what..?
Lenticular
What factors determine the level at which a cloud bases forms?
Humidity and dewpoint temperature
Unstable air over a mountain could yield what cloud?
Cumuliform
Stable air over a mountain could yield what cloud?
Lenticularis, stratus or stratocumulus
A warmer, drier wind on the lee side of a mountain describes what effect?
Foehn
Describe the foehn effect
Cloud forms on windward side of mountain
Air now drier and dewpoint temp less, cloudbase higher on leeward side
Drier and warmer wind on leeward side
Why does foehn effect result in drier, warmer air
Dry leeward air descends at DALR, which is a greater rate than the SALR-air on windward side
Two large masses of differing temp air meet, what undercuts the other?
The warmer air will be undercut by the cooler air
What is the name given to the boundary layer between two air masses?
Front
What cloud usually precipitates in a gradual way over a long period?
Stratiform
Showers only fall from what clouds
Convective cumuliform clouds
Drizzle is usually associated with what kinds of cloud?
Thick, overcast stratus cloud
In order of coverage, what are the cloud abbreviations used in METAR and TAF?
SKC, FEW, SCT, BKN, OVC
What kind of air has more potential to carry more water before saturation?
Warmer
A parcel of air has warmed in contact with the earth’s surface. What happens?
It will rise and cool adiabatically
Orographic uplift of unstable air is likely to cause what cloud?
Cumuliform
Orographic uplift of stable air is likely to cause what cloud?
Stratiform
What is the name of visibility between a pilot and the ground?
Slant visibility
What makes visibility reduce?
Particles suspended in the air
Haze produced by sea salt has what appearance?
Whitish
Salt particles from sea spray can attract water vapour (and reduce visibility) at humidity as low as…?
70%
Why does flying towards the moon give greater visibility?
Silhouettes of objects can be seen better
What does a temp inversion do to convection?
It stops vertical convection currents because of the layer of warmer air above
Inversions usually occur during what weather systems?
High pressure
Why does smog occur during a temp inversion?
Particles cannot mix throughout the atmosphere so they form a smog
Minimum humidity for mist/fog
95%
Visibility below 1km is…?
Fog
Poor visibility above 1km is called?
Mist
What conditions make the formation of radiation fog likely?
Cloudless night
Moist air
Light winds
Why are cloudless nights conducive for fog buildup?
Allows surface to cool which cools the air near it
Why do light winds help the formation of fog?
Resupply of moisture from the atmosphere to condense on the ground
Does the proportion of oxygen reduce with altitude?
No, pressure does
What is terrestrial radiation?
Long wave radiation emitted by earth that heats the atmosphere?
What usually heats the atmosphere?
Terrestrial radiation
Density equation
Mass/Volume
What is a trough?
Area of low pressure
Weather associated with a trough?
Increasing cloud and risk of precipiation
What is a col?
Area of widely spaced isobars between two highs and two lows
Weather associated with the col?
Light winds
When do altimeters over-read?
As the aircraft moves into lower pressure
Why do altimeters over-read in lower temperatures?
Density increases
Snow generally comes from what clouds?
Cumuliform
Most common type of adiabatic change?
Rising air expanding and cooling/sinking air condensing and warming
Why is SALR less than DALR?
Condensation releases latent heat energy which reduces the rate
What is the ELR like in stable conditions?
Less than 1.5 degrees per 1000ft
What is the ELR like in unstable conditions?
Greater than 3 degrres per 1000ft
If the ELR is between 1.5°C and 3°C the stability of the atmosphere will depend on…?
The moisture of the air
If the air is wet the atmosphere is unstable, whereas if it is dry it is stable. This is known as
Conditional Stability
Conditional Stability can be described as what?
Determining the stability of the air by the moisture of the air
Air Mass: Arctic Maritime
Wet cold air bringing snow in winter
Air Mass: wet cold air bringing snow in winter
Arctic Maritime
Air Mass: Polar Continental
Cold, dry, giving clear skies and frost in
winter and cool weather in summer
Air Mass: Cold, dry, giving clear skies and frost in
winter and cool weather in summer
Polar continental
Air Mass: Polar Maritime
Cold, wet, unstable air giving showers
and thunderstorms
Air Mass: Cold, wet, unstable air giving showers
and thunderstorms
Polar Maritime
Air Mass: Tropical Continental
Warm, dry air giving hazy and sometimes
dusty days, can be the source of the most
severe thunderstorms over the UK.
Air Mass: Warm, dry air giving hazy and sometimes
dusty days, can be the source of the most
severe thunderstorms over the UK.
Tropical Continental
Air Mass: Tropical Maritime
Warm, moist, stable air giving stratus,
sea fog and drizzle. This normally clears
inland in the summer.
Air Mass: Warm, moist, stable air giving stratus,
sea fog and drizzle. This normally clears
inland in the summer.
Tropical Maritime
Warm front: Cloud base
Gradually lowers, 600nm ahead of front at surface
Warm front: pressure
Pressure decreases and is stable once front has passed
Warm front: temperature
Temp and dewpoint rise
Warm front: wind
Veers
Warm front: aftermath
Low stratus and drizzle
Cold front: speed
Cool air moves more quickly than warmer air ahead
Cold front: stability
Rising warm air causes instability
Cold front: relation to warm front
Undercuts warm front
Cold front: clouds
Cumuliform clouds
Cold front: wind
Veers
Cold front: temperature
Temp and dewpoint decrease
Cold front: pressure
Falls then rises rapidly after front has passed
Global circulation results in what characteristics at the equator?
Hot rising air
Global circulation results in what characteristics at the poles?
Cold descending air
Occluded front: wind
Veers sharply
Occluded front: pressure
Drops rapidly then rises rapidly after front has passed
A cold occlusion results in what?
Cold front conditions at the surface
A warm occlusion results in what?
Warm front conditions at the surface
Danger of occluded front
Embedded CB in ST
3 conditions required for thunderstorms
Instability, high humidity and trigger action
What kind of instability causes thunderstorms?
ELR greater than 4 degrees per 1000ft
Three stages of a thunderstorm
Cumulus
Mature
Dissipating
Thunderstorms: cumulus stage
Strong updrafts
Rapid vertical growth
Thunderstorms: Strong updrafts, rapid vertical growth
Cumulus stage
Thunderstorms: mature stage
Updrafts
Severe downdraughts create microbursts, gusts and roll cloud.
Thunderstorms: Updrafts
Severe downdraughts create microbursts, gusts and roll cloud.
Mature stage
Thunderstorms: dissipating stage
Downdraughts
Precipitation
Thunderstorms: downdraughts, precipitation
Dissipating stage
How are Mountain Waves denoted in met reporting?
MTW
Is the relationship between altitude and pressure linear?
No
Moist air is usually associated with what system?
Low pressure system
Why does moist air weigh less than dry air?
Water vapour weighs less than dry air
Why is moist air related to low pressure systems?
Moist air exerts less pressure on the Earth’s surface than dry air
What is the main source of heat energy in the atmosphere?
Radiation
What is insolation?
Earth’s surface being heated by the sun
Typical vertical movement in low pressure?
Upwards
Typical vertical movement in high pressure?
Downwards
Drawback to the ‘better weather’ advantage in high pressure systems?
Lower visibility
How is an air mass classified?
Temperature then humidity
What causes areas of high and low pressure?
Uneven surface heating (mainly)
Why may wind direction and runway headings not match up?
Runways use magnetic, wind uses true north
ATC-issued wind direction is given in what format?
Magnetic heading
Effect of altitude on wind direction means the bearing of the wind does what?
Reduces the closer to the surface it gets
Effect of altitude on wind direction: bearing of the wind reduces because of..?
Coriolis effect reducing
Why is there less difference between surface wind and aloft during the day?
More mixing
Coriolis force is stronger so surface wind more aligned with aloft
If the surface wind is stronger, what does this do to its relationship with the coriolis effect?
It makes the Coriolis effect stronger (so backs less and veers more)
What causes mixing of surface air and aloft winds during the day?
Convection currents
Reason for little or no turbulence during the night near the surface?
Smooth deceleration of air between winds aloft and surface wind
What is Boyles Law?
At constant temp, volume of gas is inversely proportional to pressure
What is Charles Law (gas)
At constant pressure, volume of a gas is directly proportional to its temperature
What element/factor of the atmosphere is most significant for aircraft performance?
Air density
What is QNE?
Height of an aerodrome threshold at 1013.2hPa
What is the name of an air mass that is descending?
Subsidence
How does a subsidence cause a temperature inversion?
Descending air warms up and acts as a lid on pollutants beneath it
What causes more significant altimetry errors? Temp change or pressure change?
Pressure
Why would a moist parcel of air rise?
Water vapour less dense than dry air, it is therefore lighter and so will rise
Why are SALR and DALR always the same?
Composition of gases in dry and moist air remains constant
If the ELR is above 3 degrees per 1000 ft (DALR), what occurs?
Absolute Instability
If ELR results in Absolute Instability, what happens?
Air cools at a lesser rate than surrounding atmosphere
Parcel rises in temperature relative to surrounding air
Due to warmth, its vertical motion accelerates
If ELR results in Absolute Stability, what happens?
Parcel of air’s temperature cools relative to surrounding air, so sinks again and returns to original place
What does pressure do to relative humidity?
High pressure means less water vapour can be accomodated
In METAR/TAF temperature readings, what rounding is used?
x.0 - x.4
In terms of stable and unstable atmosphere, we can think of what two kinds of respective clouds?
Layered and heaped
Why are layered clouds associated with stable atmosphere?
Large scale ascent of air
Why are heaped clouds associated with unstable atmosphere?
Localised vertical lifting
What cloud produces a halo?
Cirrostratus
What are the white streaks on altocumulus?
Virga
Rule of Thumb for calculating cloud base formation?
(Temp - Dewpoint) x 400
Why do stratiform clouds produce light precipitation?
They have weak vertical currents and little extent
Why do cumuliform clouds produce heavier precipitation?
They have large vertical currents due to their larger extent
Metar code: SG
Snow Grains
Metar Code: Snow Grains
SG
Metar Code: GR
Hail
Metar Code: Hail
GR
Metar Code: PL
Pellets
Metar Code: Pellets
PL
Metar Code: IC
Diamond Dust
Metar Code: Diamond Dust
IC
Metar Code: SQ
Squalls
Metar Code: Squalls
SQ
Metar Code: NIL
No precipitation
Metar Code: No Precipitation
NIL
Metar Code: MON
Mountainous Regions
Metar Code: Mountainous Regions
MON
Metar Code: Over Land Regions
LAN
Metar Code: LAN
Over Land Regions
Metar Code: Over Coastal Regions
COT
Metar Code: COT
Over Coastal Regions
How is sleet indicated in UK METARS etc?
RASN
What does RASN indicate in the UK?
Sleet
What is the minimum cloud thickness for rain to occur?
4000ft
Why does more light (rising sun) make mist worse for visibility?
More light becomes reflected
When is radiation fog most likely?
At dawn when the ground temp is lowest
Radiation fog: if the wind is too light (less than 2kt), what happens?
Dew forms instead
Radiation fog: if the wind is too strong (>10kt)m what happens?
Low cloud forms instead
Radiation fog: the wind speed is directly proportional to…?
Cloud base
Radiation fog: rule of thumb for wind speed and cloud base
8kts = 800ft, 10kts = 1000ft etc
Why is radiation fog more likely to occur in autumn?
Diurnal temp variation is greatest
When is diurnal temp variation greatest?
Autumn
Metar Code: FU
Smoke
Metar Code: Smoke
FU
Metar Code: Fog
FG
Metar Code: FG
Fog
Metar Code: Mist
BR
Metar Code: BR
Mist
Metar Code: BL
Blowing
Metar Code: Blowing
BL
Metar Code: SA
Sand
Metar Code: Sand
SA
Metar Code: MI
Shallow
Metar Code: Shallow
MI
Metar Code: PR
Banks
Metar Code: Banks
PR
Metar Code: BC
Patches
Metar Code: Patches
BC
Metar Code: SS
Sandstorm
Metar Code: Sandstorm
SS
Metar Code: PO
Dustdevils
Metar Code: Dustdevils
PO
Metar Code: UP
Unidentified Precip
Metar Code: Unidentified Precip
UP
What unit of measurement is used for visibility?
Metres
CAVOK refers to clouds not below…?
5000ft
Does CAVOK mean no cloud at all?
No, just none below 5000ft
2 main causes of low pressure systems
Unstable air rising
Air being less dense due to water vapour
What type of front moves the fastest?
Cold
What is a stationary front?
Where warm air and cold air reside next to eachother
Why do occluded fronts result in prolonged rain and poor visibility?
The fronts are slower moving
Why does severe weather occur in a trough?
Increased mixing and lifting forces where isobars are closer together
High pressure systems are known as what?
Anti-cyclones
Why are winds usually slack in a high pressure system?
Isobars are widely spaced
Col in summer typified by what?
Moist air and little movement (wind)
Col in winter typified by what?
Little movement (wind) can cause low cloud and poor visibility
What happens to the cloud base as a warm front approaches?
It lowers
Why does icing occur even if an aircraft flies into above-zero water droplets?
The airframe may be sub-zero and will freeze the droplets
In what form does ice begin as in the icing process?
Large super-cooled water droplets
What is rime ice?
Impact ice
How is rime ice formed?
Water droplets impacting the air frame
How is clear ice formed?
Water droplets flow backward over air frame after rime ice formed
Why is clear ice formation so dangerous?
Reaches parts of aircraft unprotected by anti-ice systems
What type of icing is typically seen on the ground structures?
Hoar frost
How is hoar frost formed?
Sublimation
How does hoar frost form on an aircraft?
Aircraft cooled by flying through cold air mass
Aircraft enters warm air and sublimation occurs
Does hoar frost form in clouds?
Not always
What icing occurs when a warm front meets a cold air mass?
Freezing rain
How does freezing rain form in fronts?
Super-cooled droplets fall from warm air into cool and instantly freeze
Carb Icing: what happens to fuel/air as it passes through the venturi?
Pressure reduces
Dewpoint reduces
Air’s water condenses
Fuel evaporation reduces air temp further due to energy required
Why is carb ice more likely on warm days?
Warm air has the ability to hold more moisture
What is the dominant factor in causing carb icing?
Humidity
Why does the engine sometimes run more roughly after carb heat has been applied?
Ice melts into water which enters the system
Why is rime ice opaque?
It is trapped air
Rime ice is trapped air. This gives it what characteristic?
Opaque
What are the optimum conditions for a thunderstorm to form?
Hot humid atmosphere
For thunderstorms, when is TCU used instead of CU?
When a thunderstorm is taller than it is wide
What causes lightning and thunder in a thunderstorm?
Air current friction
What direction does a thunderstorm’s anvil point?
In direction of wind aloft
Thunderstorms: during the dissipating stage, what causes the updrafts to reduce?
Falling precipitation
Thunderstorms: during the dissipating stage, why does a flat top occur?
Temperature inversion
Thunderstorms: when the anvil becomes well-defined, what does this indicate?
Dissipating stage and end of the cells life
How does a supercell occur?
When winds aloft move precipitation away from the up-draughts
How is a supercell self-sustaining?
Supply of moist air is present
What causes a thunderclap?
Sudden massive expansion of air around lightning bolt due to sudden increase in temperature
A sudden massive expansion of air around lightning bolt due to sudden increase in temperature causes what?
Thunder
What instrument will give unreliable readings in the vicinity of a thunderstorm?
ADF
Why does the ADF give unreliable readings near a thunderstorm?
Lightning has a broad Radio Frequency spectrum
Rule of thumb for thunderstorm distance
5 second delay between thunder and lightning = 1nm distance
What factor determines a thunderstorm’s direction?
Winds aloft, not surface winds
Do thunderstorms travel in the prevailing surface wind direction?
No
Thunderstorms tend to be severe above what dewpoint?
20 degrees
A plane flying towards a depression will experience what? (In the NH)
Starboard drift
What moves faster across the earth? Highs or lows?
Lows
Why do clouds form in a depression?
Rising air is cooled
Why is visibility good in low pressure?
Vertical motion of air carries away suspended particles
What kind of visibility is associated with a low?
Good
What is a V-shaped extension of isobars from a depression called?
Trough
A trough on a chart resembles what?
V-shaped extension of isobars
A trough carries which two key factors for the development of CBs and storms?
Unstable air and rising air due to low level convergence
In a trough, what is a major risk associated with observing a cloud formation?
CBs may be embedded within other cloud (such as stratiform)
An aircraft flying towards an anticyclone will experience what?
Port drift
What is the stability of subsiding air?
Very stable
Subsiding air in an anticyclone means the air is what…?
Very stable
What causes mountain waves and windshear to exist on the outskirts of an anticyclone?
Temperature inversion combines with stronger winds
Temperature inversions and strong winds on the outskirts of an anticyclone can produce what?
Windshear and mountain wave
U-shape extension of isobars from a high is called what?
Ridge
What is the anticyclone equivalent of a trough?
Ridge
Venturi effect means high pressure, low speed becomes what when constricted?
Low pressure, high speed
Where can the venturi effect exist in the air?
Mountain wave
Mountain wave venturi effect results in what?
Wind aloft speeds increase, pressure decreases
Venturi effect in mountain wave has wgat effect on safe flight?
Altimeter may over-read due to lower pressure
Icing: what cloud is specifically risky for icing in mountain flying?
Lenticular clouds
European Air Circulation: winter pressure
Low pressure in Atlantic, High in continent
European Air Circulation: winter jet stream
More southerly than usual
European Air Circulation: summer pressure
High pressure in Atlantic
European Air Circulation: high pressure in Atlantic summer is known as what?
Azores HIgh
When does an Azores High usually occur?
Summer
Which air mass is generally responsible for snow over the UK?
Arctic Maritime
Arctic Maritime is an air mass that can bring what event in the UK?
Snow
‘Continental’ in air mass description denotes what
Dry, and therefore stable
F215 provides weather for what vertical space?
Ground to 10,000ft
Typical F215 forecast validity?
9 hours
F215 terminology: phenomenon coverage >50%
Frequent
F215 terminology: phenomenon coverage 25-50%
Occasional
F215 terminology: phenomenon coverage <25%
Issolated
F215 chart provides info on what in the UK?
Significant weather
Significant weather in the UK is forecasted by the Met Office in what publication?
F215
F214 chart provides info on what in the UK?
Spot wind and temperatures
F214s are issued every…hours?
6 hours
What two probability codes are used in the UK for TAFs?
PROB30 and PROB40
In a TAF, PROB30 is generally understood as…?
Might happen
In a TAF, PROB40 is generally understood as…?
Will happen
For METARS, NOSIG means what?
No significant change during the two hours after observation time
For METARS, NOSIG has what time forecast
2 hours
Infra-Red satellite shows what?
The temperature of clouds
In IR-satellite, how is temperature indicated?
The lighter the colour, the lower the temperature
VOLMET broadcasts METARs or TAFs?
METARs
How is VOLMET broadcast?
On VHF continuously
Where does the tropopause begin at the equator?
18km (60,000ft)
Where does the tropopause begin at the poles?
9km (30,000ft)
What weather conditions might be associated with a Col in the winter months in the UK?
Low Cloud, light winds, Poor visibility (possibly even fog)
