General / Misc Met stuff (Met) Flashcards
How is cloud cover described?
The basic unit is the octare, which represents the number of eighths of the sky covered by cloud. 0 octares is called no cloud, 1 to 2 is called few clouds, 3 to four is scattered clouds, 5 to 7 is broken cloud, and 8 is complete cloud cover.
What are WAFCs, and where are they?
World Area Forecast Centers, the centers for coordinating meteorological aviation information across the world. Located in London, which handles the eastern hemisphere, and Washington, which handles the western hemisphere.
What is an RSMC, and where is the UK’s?
A Regional Specialised Meteorological Centre. The UK’s is in Exeter.
What is “spread”?
The current temperature minus the dew point. This means that, if the current temperature is less than the dew point, the spread will be negative. Always in Kelvin.
What is a density altitude?
It is the altitude you would be at if your current density were the same, but you were in an ICAO standard atmosphere.
What are the two main types of thermometer, besides mercury/alcohol capillary thermometers, and how do they work?
Bimetallic thermometers, which measure how far a metal bends or droops with temperature change, or resistance thermometers, which measure how the conductivity of a substance changes as its temperature varies.
What are the five mechanisms by which energy may be transferred from one place to another within the atmosphere?
Compression/expansion Evaporation/condensation/freezing/melting Conduction/diffusion Convection/advection Radiation
What is an atmospheric inversion? What does it cause?
An area of the atmosphere in which the temperature is rising with altitude instead of falling. It causes a ceiling of warm air which blocks convection, leaving anything carried by said convection at that height.
What it is called if a barometric instrument is giving an incorrect reading because it is located somewhere which is being disturbed by the airflow of the plane’s motion?
Position error.
What is dynamic pressure error?
The errors caused in barometric instruments by small, localised areas of non-typical pressure.
What is the name of the types of error in barometric instruments caused by mechanical tolerances, shortcomings, or calibration issues?
Instrument error.
What is the name for errors in barometric instruments caused by the pilot failing to re-adjust the instrument when going from place to place, or over a significant degree of time?
A pressure error.
What is QFF?
The pressure at mean sea level under current atmospheric conditions (i.e. adjusted for temperature, as opposed to QNH).
What is QNE?
The pressure setting which a given elevation would have, were the QNH 1013.25hPa.
Who might want to fly by QFE rather than QNH?
Acrobatic flights performing close-to-ground maneuvers, who need to know how much space they have left, or flights carrying skydivers, who may well want to know if they are far enough from the ground yet or not.
What are MSA and MVA, and what is the difference between them?
Minimum Safe Altitude is the lowest you can fly without breaking obstacle clearance rules. Minimum Vectoring Altitude is MSA adjusted for temperature. Charts usually have a warmest-expected MVA and coldest expected MVA alongside it in brackets.
What is the difference between fog and mist?
Both are ground-level airborne moisture which obscures visibility. Fog results in <1km visibility, mist is 1km
What are the possible problems caused by fog?
Airport reduced capacity due to higher seperation.
Pilots need to get in place earlier to establish their bad weather stuff.
The localiser can be disturbed by the near passage of other craft, and this is important because the landing must be done by auto-pilot guidance.
Airports can close altogether if they are not rated for Cat II or III operations.
Increased go-arounds and diversions.
Planes can get a bit lost taxiing.
What are the sensitive and critical zones, and why are they important in meteorological terms?
They are the areas of an aerodrome in which large objects cannot remain while ILS is in use, and cannot be while Cat II and III operations in place, respectively. They are meteorologically important because they need to be observed during times of low visibility.
How large is the sensitive zone?
16 degrees cone from the localiser, centered over the middle of the runway, with a minimum width of 135m either side of the runway’s centre line, and 135m past the end of the runway.
What conditions cause radiation fog?
Temperature drop at the end of the day causing water to leave the atmosphere. The following morning, the sun evaporates said water, but the air is not yet warm enough to contain it. Most common in winter, and only happens over continents. Requires low winds and clear sky.
What conditions cause advection fog?
Warn, moist air being blown into a patch of cool air, which then causes the moisture to condense. Usually occurs at the seaside, where the air above the land is cooler than the sea in the autumn, and warmer than the sea in the spring. Requires a breeze from warm to cold.
What conditions cause mixing fog?
One weather front moving into another of a different temperature. This causes the moisture in the cooling air to condense. Can happen basically anywhere, and most common during winter.
What are the typical thicknesses of radiation, advection and mixing fog?
100-200m, 500-1000m, and basically 1000-5000m+, respectively.
What are the meteorological codes for mist and fog?
BR is mist, FG is fog, MIFG is shallow fog, and BRFG is patches of fog.
How far above the ground should an anemometer be?
10 meters.
Which wind direction reports are given with respect to true north, and which are given with respect to magnetic north?
Tower and ATIS reports are in magnetic north, everything else uses true north.
