Transport Canada Flight Dispatcher Meteorology Exam flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Standard sea-level pressure

1013.25 hPa or 29.92 inHg, the reference pressure used to calibrate altimeters and define pressure altitude and flight levels.

Troposphere

Lowest atmospheric layer where temperature decreases with height, containing about 80% of atmospheric mass and nearly all weather; its top is the tropopause.

Standard lapse rate

Average tropospheric temperature decrease of about 1.98 °C per 1000 ft, or 6.5 °C per kilometre, used as the ISA reference lapse rate.

QNH

Altimeter setting that causes the altimeter to read elevation above mean sea level at the aerodrome when the aircraft is on the ground.

Density altitude

Pressure altitude corrected for temperature and humidity; high density altitude reduces aircraft performance and increases takeoff and landing distances.

High-to-low altimeter error

Flying from high pressure to low pressure without resetting the altimeter causes the aircraft to be lower than the indicated altitude.

Dew point

Temperature to which air must be cooled at constant pressure and moisture content for saturation to occur and condensation to begin.

Lifting condensation level

Height at which rising air cools to its dew point and cloud forms; roughly 400 ft per 1 °C of surface temperature-dew point spread.

Conditional instability

Atmospheric state where the environmental lapse rate lies between the dry and saturated adiabatic rates, so stability depends on whether the air is saturated.

Nimbostratus

Thick, dark, layered cloud producing continuous steady precipitation; associated with stable air and approaching warm fronts.

Cumulonimbus

Deep convective cloud with strong updrafts and downdrafts, producing thunderstorms, hail, icing, turbulence, and microbursts; avoid by at least 20 nautical miles.

Freezing rain

Precipitation that falls as liquid and freezes on contact with subfreezing surfaces; it indicates a warm layer aloft and severe airframe icing risk.

Cold front

Boundary where cold air advances under warm air; steep slope, narrow band of heavy showers and thunderstorms, and rapid clearing behind.

Warm front

Boundary where warm air rides over cold air; shallow slope, broad layered cloud, steady precipitation, and gradual clearing after passage.

Occluded front

Front formed when a cold front overtakes a warm front, lifting the warm sector aloft; weather combines warm-front and cold-front characteristics.

Mid-latitude cyclone

Large low-pressure system that forms along a frontal zone in middle latitudes and evolves through wave, open, occluded, and decay stages.

Upper-level trough

Elongated region of low heights aloft associated with rising motion, surface pressure falls, and cyclogenesis downstream of the trough axis.

Jet stream

Narrow band of strong upper-level wind near the tropopause; it steers surface systems and is associated with clear-air turbulence and wind shear.

Microburst

Small, intense downdraft less than 2.5 nautical miles across that produces a damaging outflow and severe low-level wind shear.

Clear-air icing

Supercooled liquid water in clouds at temperatures between 0 °C and about −20 °C that freezes on aircraft surfaces and increases stall speed.

Clear-air turbulence

Turbulence in cloud-free air, most often near jet-stream cores and strong wind shear; it is not detectable by radar or satellite.

Foehn wind

Warm, dry downslope wind on the lee side of a mountain barrier, produced by adiabatic warming as air descends after crossing the ridge.

Sea breeze

Daytime onshore wind caused by differential heating of land and sea; the sea-breeze front can trigger thunderstorms near the coast.

Mountain wave

Oscillating airflow downstream of a mountain ridge, producing severe turbulence, lenticular clouds, and strong downdrafts on the lee side.

METAR ceiling

Lowest broken or overcast layer, or vertical visibility into an obscuration; reported in feet above ground level.

SPECI

Unscheduled observation issued when significant weather changes occur between routine METARs, such as ceiling, visibility, or thunderstorm criteria.

PIREP

Pilot report of in-flight weather such as turbulence, icing, or wind shear, transmitted as UA routine or UUA urgent reports.

TAF

Terminal aerodrome forecast of wind, visibility, weather, and sky cover for a specified period, using BECMG, TEMPO, and FM change groups.

SIGMET

Advisory for severe weather such as severe turbulence, severe icing, volcanic ash, or tropical cyclones that affects flight safety.

AIRMET

Advisory for moderate icing, moderate turbulence, or extensive low ceilings and visibility that are below SIGMET thresholds.

Surface analysis chart

Chart showing isobars, pressure centres, fronts, and station models at a given time, used to identify synoptic features and frontal positions.

Significant weather chart

Chart depicting fronts, jet streams, turbulence, icing, and cumulonimbus areas for flight planning at selected altitudes.