DGCA CPL Aviation Meteorology 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 (29.92 inHg), the reference pressure for the International Standard Atmosphere and for QNE altimeter setting above the transition altitude.

ISA temperature lapse rate

1.98 °C per 1000 ft (6.5 °C per km) from sea level up to 36,090 ft, above which the standard atmosphere is isothermal at -56.5 °C.

Tropopause

The boundary layer between troposphere and stratosphere, averaging 11 km (36,000 ft), higher over the equator and lower over the poles, marked by an isothermal lapse rate.

QNH

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

QFE

Altimeter setting that makes the instrument read height above the aerodrome reference point, so it indicates zero on the ground at that aerodrome.

QNE

Standard pressure setting of 1013.25 hPa used above the transition altitude, giving pressure altitude and standard flight-level separation.

High to low, look out below

Rule stating that flying from high pressure or high temperature to low pressure or low temperature without resetting the altimeter leaves the aircraft lower than indicated.

DALR

Dry adiabatic lapse rate of about 3 °C per 1000 ft (9.8 °C per km), the cooling rate of an unsaturated rising air parcel.

SALR

Saturated adiabatic lapse rate, roughly 1.5-1.8 °C per 1000 ft, the slower cooling rate of a rising parcel once condensation releases latent heat.

Absolutely unstable air

Condition where the environmental lapse rate exceeds the dry adiabatic lapse rate, so a rising parcel stays warmer than its surroundings and accelerates upward.

Dew point

The temperature to which air must be cooled at constant pressure to become saturated; a small temperature-dew point spread indicates high humidity and fog risk.

Temperature inversion

A layer where temperature increases with height; it traps moisture and pollutants below, gives smooth air, and often produces haze or fog.

Relative humidity

The ratio of actual water vapour pressure to the saturation vapour pressure at the same temperature, expressed as a percentage.

Cumulonimbus

A deep vertically developed cloud producing thunderstorms, hail, severe turbulence, icing, lightning and microbursts; it must be avoided by a wide margin.

Nimbostratus

A thick low stratiform cloud giving continuous steady precipitation, typical of stable air ahead of a warm front.

Supercooled water

Liquid cloud droplets remaining unfrozen at temperatures between 0 °C and about -20 °C; they freeze on impact with an airframe, causing icing.

Cloud base estimate

Approximate convective cloud base in feet equals the surface temperature minus dew point (the spread) multiplied by 400.

Geostrophic wind

Wind flowing parallel to straight isobars in balanced flow, with low pressure to the left in the Northern Hemisphere and speed increasing as isobars tighten.

Buys Ballot's law

With your back to the wind in the Northern Hemisphere, low pressure lies to your left; in the Southern Hemisphere, low pressure lies to your right.

Sea breeze

A local daytime wind blowing from sea to land because the land heats faster than the water; it is strongest in the afternoon.

Katabatic wind

A downslope wind caused by cold dense air draining downhill at night, common in valleys and over ice sheets.

Föhn wind

A warm dry downslope wind on the lee of mountains; descending air warms at the dry adiabatic rate, about 3 °C per 1000 ft.

Cold front

The leading edge of advancing cold air with a steep slope, producing a narrow band of heavy showery precipitation, squalls and rapid clearing after passage.

Warm front

The leading edge of advancing warm air with a shallow slope, producing a wide band of stratiform cloud and steady precipitation ahead of it.

Occluded front

A front where a cold front overtakes a warm front, lifting the warm air aloft and producing complex cloud and precipitation.

Thunderstorm mature stage

The stage with both updraughts and downdraughts, precipitation reaching the ground, lightning, hail and the greatest turbulence hazard.

Clear air turbulence

Turbulence occurring without visible cloud, typically near jet streams, the tropopause and zones of strong wind shear.

Microburst

A strong localized downdraught producing a damaging outflow at the surface, creating severe low-level wind shear hazardous on approach and departure.

Radiation fog

Fog formed on clear calm nights when the ground cools by radiation and the air above reaches its dew point.

METAR

A routine aerodrome weather report issued typically hourly, giving wind, visibility, weather, cloud, temperature, dew point and QNH.

TAF

An aerodrome forecast valid typically 9-30 hours, using FM, BECMG and TEMPO groups to describe expected changes.

SIGMET

A warning of significant weather hazardous to all aircraft, such as severe turbulence, severe icing, thunderstorms or volcanic ash.