Meteorology Flashcards
What are the 5 layers of the atmosphere?
Exosphere
Thermosphere
Mesosphere
Stratosphere
Troposphere
Troposphere height
7km
Stratosphere height
50km
Mesosphere height
85km
Thermosphere height
650
Exosphere height
10,000
Troposphere characteristics
fall of density, pressure and temperature with height
presence of virtually all atmospheric water vapour
marked variation in space and time in the vertical and horizontal motion
Stratosphere characteristics
biggest concentration of ozone
extremely dry air
water trapped below in troposhere
no precipitation
Mesosphere characteristics
no heat source
keeps temp decreasing down to minimum in atmosphere
-80 to -100 degrees Celsius
Thermosphere characteristics
very high temperature increase
1200 to 1700 degrees Celcius
What does the bombardment of high energy radiation from the sun cause in the atmosphere?
Many of the molecules and atoms to become ionised
Nitrogen%
Oxygen%
Argon, helium, hydrogen%
78% , 21% , 1%
The atmosphere is ____ ____ to sun’s radiation
relatively transparent
Where is most of the energy from the sun absorbed?
earth’s surface
What height does temperature decrease with height go up to?
36,000ft
What temperature decrease with height called?
Lapse rate
What is the average temperature lapse rate in the atmosphere?
1.98c/1000ft
Pressure =
Density x Depth
what do pressure readings vary according to?
density of the atmosphere above that point
What does density vary according to?
air temp & water content
What is MSL pressure?
1013.25 hPa
what are the rates of change of pressure with increasing height?
1 hPa = 30ft to MSL
1 hPa = 50ft at 20,000ft
1 hPa = 100ft at 40,000ft
What is density?
the mass in a unit of volume
What does air density affect?
ROC
Drag on an aircraft
Aerodynamic forces on propellers
Pressurisation
What are the tools used for met data? (8)
Thermometers
Radar systems
Barometers
Rain gauges
Wind vanes/ Anemometers
Transmissometers
Hygrometers
Satellites
Atmospheric pressure is measured in… ?
Inches of mercury (ins)
Millibars (mb)
Hectopascals (hPa)
What does a mercury barometer suffer from?
Index error
temperature error
gravity error
What does Aneroid mean?
Without liquid
How does an aneroid barometer work?
It uses a partially evacuated metal capsule that reacts to changes in air pressure by expanding or contracting.
What does the aneroid barometer suffer from?
Index error but is provided with a correction chart
ISA
International standard atmosphere
ISA at MSL
Temp
Pressure
Density
+15 degrees Celsius
1013.25 hPa
1.225 kg/m3
ISA lapse rate above MSL
1.98c/1000ft up to 11km
0c/1000ft from 11km to 20km
Precipitation can be reported as?
Present, significant or recent
Specific heat capacity
heat required to raise the temperature of 1kg of a substance by 1c
what is radiation?
transfer of heat between bodies that aren’t in contact
what is conduction?
transfer of heat between bodies that are in contact
What is convection?
transfer of heat by vertical movement
What is diurnal variation?
Change within the day
Diurnal variation- Surface
Variation is greater over land than sea
Diurnal variation- windspeed
wind causes turbulence that spreads cooling effect of the earth through a greater depth of air
Diurnal variation- clouds
reduces heat loss
what is inversion?
certain conditions may cause temperature to increase with height or remain the same in an isothermal layer
How do you measure temperature?
thermometer
Celcius to fahrenheit
9*c/5 + 32
Fahrenheit to celcius
5(F - 32) / 9
Kelvin scale -
Theoretical absolute zero-
Freezing point H2O
Boiling point H2O
0k (-273c)
273k
373*k
Fahrenheit-
Freezing point
boiling point
32f
212f
What happens water changes state?
Latent heat locks heat into, or gives heat back to the atmosphere
What happens when saturated air is cooled?
water vapour content will be too great and visible droplets will appear. (condensation)
What is sublimation?
process where ice and snow changes into water vapour without moving through the liquid stage
What does the amount of water vapour present in the atmosphere depend on?
temperature of the air
What is dew point?
the atmospheric temperature below which water droplets begin to condense and dew can form.
What are the 4 ways air may be cooled below dew point?
Conduction
Evaporation
Adiabatic cooling
Mixing
What is latent heat?
heat required to cause a change in state
What is relative humidity?
the measurement of the amount of water vapour present in the air, relative to how much would be require to cause saturation at the temperature
How do we measure humidity?
hygrometer
What are the 2 types of hygrometer?
Hair hygrometer
wet and dry hygrometer
Why is no heat transferred within the atmosphere during the adiabatic process?
air is a poor conductor of heat
How do we calculate dew point with a wet and dry hygrometer?
Finding the difference between the dry and wet bulb temperatures
What is the adiabatic process?
as the temp of air increases, so its density decreases and if its surrounded by colder, denser air, it will tend to rise.
Dry adiabatic lapse rate (DALR)
3c/1000ft
unsaturated air rising cools at this rate
What are the 3 lapse rates?
Dry adiabatic lapse rate
saturated adiabatic laps rate
environmental lapse rate
Saturated adiabatic lapse rate (SALR)
1.5 - 2c/1000ft
saturated air rising whilst condensation is taking place.
saturation of air impacts rate
unstable atmosphere
a small perturbation to an object encounter a force which will move the object farther from its original position
Environmental lapse rate (ELR)
lapse rate at any given time or location
Conditional instability
When the ELR lies between the DALR and SALR. A parcel of dry air will be cooler at height than the environment and will sink, but a parcel of saturated air will be warmer and will continue to rise
neutral atmosphere
a perturbation to a body results in restoring or displacing force being applied, so that the body remains in its perturbed position.
Stable atmosphere
any small perturbation to a body, or a body of air, will encounter a restoring force which tends to return it to its original position
Absolutely stable atmosphere
When the ELR in a layer is less than the SALR
Absolute instability
the ELR is grater than the SALR and DALR
What are the 5 lifting processes?
frontal lifting
orographic lifting
convergence (depression)
convergence (thermal)
turbulence
what is frontal lifting?
advancing cold air forcing warm air to rise and vice versa
what is orographic lifting?
when mountains or other large geographical features force air to pass over them
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 causes vertical movement within the atmosphere
Relatively high temperature implies…
low density
High level clouds
cirrus
cirrocumulus
cirrostratus
medium level clouds
altocumulus
altostratus
nimbostratus
low level clouds
cumulus
stratus
cumulonimbus
stratocumulus
What are the associated hazards from a
Cumulonimbus cloud?
Turbulence, hail, lightning, icing, static,
windshear
What are the requirements to make a TS?
Moisture, instability, trigger
How long does a TS last normally?
Growing stage 30 mins, mature stage 30
mins, dissipating stage can last 2 hours or
can regenerate.
What does supercooled water do when it
hits an airframe?
If the airframe is below 0C it will freeze,
causes clear ice and RIME ice
When does clear ice form on an aircraft?
Transparent or translucent ice formed by
large droplets that are only just
supercooled. A large percentage of each
drop flows backwards and gradually freezes
to produce a rapid build-up of heavy thick
ice
When are we likely to get RIME Ice?
When flying through cold air and
approaching a warm front
What are the significant factors for Ice?
Temperature, Drop size, Airframe shape,
Kinetic heating, Concentration
Definition of Fog?
A suspension of small water droplets
reducing visibility below 1000m
Definition of Mist?
The same as fog except visibility is not less
than 1000m
Definition of Haze
A suspension of solid particles of smoke or
dust reducing visibility to not less than
1000m where the relative humidity is less
than 95%
How is RVR measured?
Human observer method
Instrumented RVR
What is the Human observer method?
An assessment is made counting the lights
or markers along the runway length and
calculating the distance from a calibrated
table
What is Radiation Fog?
Forms over land. On a clear night the
ground radiates heat, its temperature drops
rapidly and if the air is sufficiently moist the
layer in contact with the ground will be
cooled below its dew point and
condensation will occur. Just before dawn is
the most likely time
Requirements for Radiation Fog?
Clear sky, Land surface, Moist air, Light
wind, Long night
How does the windspeed affect Radiation
fog?
No wind – settles on ground as dew
2-8kts – thin layer of fog
8kts+ - lifts fog to form stratus cloud
How is hill fog formed?
Air moving up slopes and condensing at the
top, to form low cloud/hill fog
How is advection fog formed?
Warm air with a relatively high humidity
may be cooled enough, by contact with a
cold surface, to cause condensation
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
What is windshear?
Wind shear is a rapid change of wind speed
and/or direction over a short distance
horizontally or vertically
What is a microburst?
A microburst is a localized column of sinking
air (downdraft) within a thunderstorm and
is usually less than or equal to 2.5 miles in
diameter
Cloud Okta scale?
FEW 1-2
SCT 3-4
BKN 5-7
OVC 8
how is turbulence caused?
random fluctuations in the wind flow causing the wind to vary in speed and/or direction over a short distance
when is turbulence called wind shear?
at lower levels or in the vicinity of an airfield
Convection turbulence
caused by variations in convection currents affecting aircraft at low level and speed
The degree of turbulence present in the friction
layer depends upon…
Strength of the surface wind
The stability of the wind
The nature of the surface.
What is wind shear?
a rapid change of wind speed
and/or direction over a short distance
horizontally or vertically
When is a pilot 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 the vicinity of standing waves.
-Flying near, and especially underneath, a
cumulonimbus
What does low level wind shear cause?
changes of wind velocity along an
aircraft’s flight path that occur faster than it can
accelerate or decelerate to compensate for them.
What is a microburst?
A microburst is a localized
column of sinking air within a
thunderstorm and is
usually less than or equal
to 2.5 miles in diameter
(LLWSAS)
low level wind shear alert system
What does LLWSAS consist of?
five anemometers situated around
the airfield perimeter and one centrally located
What is a low level wind shear alert based on?
-Mean surface wind of at least 20kts.
-A difference between surface and 2000ft wind
speeds of at least 40kts.
-Thunderstorms or heavy showers within 5nm of
the airfield.
-Pilot reports of local wind shear conditions.
Downdrafts (macrobursts)
4 km (2.5 miles) in diameter and can produce
winds as high as 60 metres per second, or 215 km
per hour (200 feet per second, or 135 miles per
hour)
What is clear air turbulence?
turbulence that occurs without any cloud to
indicate its presence
Where CAT normally present?
upper troposphere or lower stratosphere
How can a pilot detect CAT?
observing the significant change in outside air temperature that will be experienced when flying through the frontal boundary between warm and cold air.
What is an air mass?
An air mass is a volume of air with many uniform
characteristics extending over a large region.
Equatorial masses are:
very warm
Tropical and polar masses are:
Warm and cold respectively
Arctic is reserved for:
VERY COLD air masses that originate
in the Arctic Ocean
How are air masses classified?
based on their source region
Arctic: Very cold and humid
Polar Maritime: Cold and humid
Polar Continental: Cold and dry
Tropical Maritime: Warm and humid
Tropical Continental: Warm and dry
Equatorial: Hot and humid
Low pressure systems are known as:
depressions or cyclones
high pressure systems are known as:
anticyclones
Depressions are characterised by…
Strong winds and rising air
Measurements of a depression
1000km-2000km across, extend up from surface to tropopause
What direction anticyclones revolve?
clockwise
Anticyclones are characterised by…
Light winds and subsiding air leading to clear
skies and fine weather with no precipitation.
what is anticyclonic gloom?
A condition of low visibility associated with
anticyclones
What is a trough?
An elongated area of relatively
low surface pressure
What is a ridge?
an area of high pressure which
elongates to form a ridge of high pressure
synoptic chart
shows pressure
What is a front?
A boundary between 2 air masses
WMO
World Meteorological Organisation
WAFS
World area forecast system
SADIS
satellite distribution system
RAFC
Regional area forecast centre
MWO
Meteorology watch organisation
WAFC
World area forecast centre
VAAC
Volcanic ash advisory centre
Where is MET info derived from?
Surface Observations
Upper Air Observations
Observations from Aircraft in Flight
Observations from Satellite
What reports are available at aerodromes?
Meteorological Aerodrome Report (METAR)
Special Report (SPECI)
Terminal Aerodrome Forecast (TAF)
Aerodrome Warnings
Wind Shear Warnings
METAR
A report of actual weather conditions at a
particular aerodrome at a specified time.
For each hour or half hour
SPECI
An amendment to a METAR that is designed
to draw attention to an improvement or
deterioration of a condition that might
significantly affect aircraft operations
TAF
A concise statement of expected meteorological
conditions at an aerodrome during a specified
period
Issued in a code form.
Prepared every 3 hours for 9 hour period.
24 or 30 hour TAFS for long haul schedules are
issued at 6 hourly intervals.
Trends - for selected aerodromes are added to
METAR to indicate significant expected changes
over next 2 hours
Aerodrome warnings
Issued to aerodromes by MWO by AMHS / phone.
They relate to the following phenomena having
occurred or expected:
Gales / Strong wind warning
Squalls
Thunderstorm
Hail
Fog
Frost / Snow
Freezing precipitation
Wind Shear Reports
Windshear reports are based on recent pilot reports
of windshear on the approach or climb-out.
Pilots should give concise information concerning
wind shear conditions, whether by reference to speed
loss or gain or in terms of its effect on the aircraft.
Cancelled when aircraft reports indicate that
windshear no longer exists.
Pilot should report windshear even if already reported
or warned
MARKED TEMPERATURE INVERSION
For specific aerodromes warnings of marked
temperature inversions are issued whenever a
difference of 10°c or more exists up to 1000ft aal.
This warning is broadcast on departure and arrival
ATIS at aerodromes so equipped
SIGMET
Warn pilots of actual or anticipated weather conditions
that could affect the safety of aircraft operations.
They include the following for subsonic flight:
Active Thunderstorm Tropical Cyclone
Freezing Rain Heavy hail
Severe turbulence Severe icing
Severe mountain waves Volcanic ash cloud
Heavy dust/sandstorms
SIGMET distribution
MET office prepares SIGMET info sends to ACC/FIC.
ACC/FIC pass SIGMET to aircraft in flight if up to
500nm ahead on route or 2 hours flying time.
Valid for 4 hours and reissued if necessary
AIREP
AIRCRAFT OBSERVATIONS AND REPORTS
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.
ATIS
ATIS - AUTOMATIC TERMINAL INFORMATION SERVICE
A repetitive recording that is continuously transmitted
on a dedicated airfield VHF frequency. It transmits the
following information in plain language –
Aerodrome Status
Current weather
ATIS Information Code
MET office duties
Prepare and obtain relevant information for all
flights with which it is concerned.
Supply other meteorological information to
aeronautical users.
Display available meteorological information.
Exchange information with other met offices.
Information that is required by aerodrome and approach
control on a routine basis includes:
METAR with trend as appropriate every hour or half hour.
SPECIs as appropriate.
Aerodrome forecasts (TAF).
Aerodrome warnings.
SIGMET.
Additional information as agreed locally.
ATC will only transmit what has been supplied
by the met office - the exceptions are:
Indicated wind speed & direction.
RVR observation.
Controller observation of sudden deterioration -
inform aircraft.
Aircraft reports of weather hazards.
Cloud echoes observed on radar.
Official met observation (certificated).
Unofficial met observation.
Once a flight is airborne, pilots can obtain aerodrome
weather information from any of the following:
-VOLMET broadcasts.
(see GEN 3.5)
-Automatic Terminal Information Service (ATIS)
broadcasts.
-By request to an ATS Unit but whenever possible only if the information required is not available from a broadcast.
