Brunei DCA CPL(A) Meteorology flashcards

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

Tropopause

Boundary between troposphere and stratosphere where temperature stops decreasing with height; about 36,000 ft at the equator and 20,000 ft at the poles.

ISA sea level values

ICAO Standard Atmosphere at mean sea level: pressure 1013.25 hPa, temperature +15 °C, density 1.225 kg/m³, with a lapse rate of 1.98 °C per 1000 ft in the troposphere.

Pressure altitude

Altitude indicated when the altimeter subscale is set to 1013.25 hPa. It is the datum used for flight levels and for computing density altitude and aircraft performance.

QNH

Altimeter setting that makes the instrument read elevation above mean sea level when the aircraft is on the ground at the reference point.

QFE

Altimeter setting that makes the instrument read zero when the aircraft is on the ground at the reference point, giving height above that point.

Density altitude

Pressure altitude corrected for temperature deviation from ISA. High temperature, high humidity and low pressure all increase density altitude, degrading aircraft performance.

Altimeter high-to-low error

Flying from high pressure into low pressure without resetting the subscale causes the aircraft to be lower than the altimeter indicates, a hazard in terrain.

Dew point

Temperature to which air must be cooled at constant pressure to become saturated. A small temperature-dew point spread indicates high relative humidity and possible fog or low cloud.

Lifting condensation level

Height at which rising air reaches saturation and cloud forms; approximated as 125 m or about 400 ft per 1 °C of temperature-dew point spread.

Dry adiabatic lapse rate

Rate at which unsaturated rising air cools, about 3 °C per 1000 ft. Compared with the environmental lapse rate it determines whether the atmosphere is stable.

Saturated adiabatic lapse rate

Rate at which saturated rising air cools, about 1.5 °C per 1000 ft near sea level. Latent heat release makes it smaller than the dry adiabatic lapse rate.

Conditional instability

State in which the environmental lapse rate lies between the saturated and dry adiabatic lapse rates, so stability depends on whether the rising air is saturated.

Cumulonimbus

Deep convective cloud with strong updraughts and downdraughts, severe icing, hail, lightning and microbursts. Aircraft should avoid it by at least 20 nautical miles.

Radiation fog

Fog formed by nocturnal cooling of moist air over land under clear skies and light winds. It usually forms in the early morning and dissipates after sunrise.

Advection fog

Fog formed when warm moist air moves over a colder surface and is cooled to its dew point. It can persist day and night and is common over the sea.

Freezing rain

Rain that falls through a sub-freezing layer and freezes on impact. It indicates severe icing potential for aircraft flying in or below the cold layer.

Cold front

Leading edge of advancing cold air with a steep slope. Passage brings a narrow band of heavy showery rain, wind veer, falling temperature and improving visibility.

Warm front

Leading edge of advancing warm air with a shallow slope. It brings extensive stratiform cloud and steady rain ahead of the surface position, with slow wind veer and rising temperature.

Occluded front

Front formed where a cold front overtakes a warm front and lifts the warm sector clear of the surface. It often produces complex cloud and widespread precipitation.

Anticyclone

High-pressure system with descending air, subsidence inversion, light winds and clear skies. Visibility is good aloft but haze or fog may form near the surface.

Geostrophic wind

Wind that flows parallel to straight isobars in balance between pressure gradient and Coriolis forces. It is stronger where isobars are close together and weaker at low latitudes.

Buys Ballot's law

In the Northern Hemisphere, with your back to the wind, low pressure lies to your left. The rule reverses in the Southern Hemisphere.

Sea breeze

Daytime wind from sea to land caused by differential heating, with cooler denser air over the water moving inland. It is strongest in the afternoon and can reach 20 knots.

Mountain wave

Oscillating airflow downwind of a ridge in strong, stable cross-mountain flow. It produces severe turbulence, lenticular cloud and strong downdraughts on the lee side.

Tropical cyclone eye

Central region of subsidence, light winds and clear sky surrounded by the eyewall, which contains the strongest winds and heaviest precipitation.

Tropical cyclone formation

Requires sea surface temperature above about 26.5 °C, low vertical wind shear, high low-level vorticity and at least 5° of latitude from the equator.

Sumatra squall

Line of intense thunderstorms that forms over the Strait of Malacca and moves eastwards, often in the early morning, bringing strong gusts and heavy rain.

Clear ice

Transparent, heavy icing formed by large supercooled droplets, often in freezing rain. It adheres strongly, spreads over the airframe and is the most hazardous icing type.

Microburst

Concentrated downdraught producing a sudden headwind followed by a tailwind change near the ground. The resulting windshear can exceed aircraft performance capability.

Clear-air turbulence

Turbulence in cloud-free air, associated with jet streams and strong wind shear near the tropopause. It is invisible to the eye and to weather radar.

METAR

Routine surface aviation weather observation, usually issued hourly. It reports wind, visibility, weather, cloud, temperature, dew point, pressure and trend.

SIGMET

Warning of weather significant to all aircraft, such as severe turbulence, severe icing, volcanic ash, tropical cyclones and severe mountain waves. It is valid for four hours.