CPL Meteorology (Sri Lanka CAA Pilot Licence Examinations) flashcards

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

Standard atmosphere sea-level pressure

1013.25 hPa, equivalent to 29.92 inHg, used as the reference pressure for pressure altitude and for the standard atmosphere.

ISA temperature lapse rate

1.98 °C per 1000 ft (about 2 °C per 1000 ft) in the troposphere up to 36,090 ft, where the tropopause begins.

Tropopause

The boundary between troposphere and stratosphere, at about 36,090 ft in ISA, where temperature stops decreasing with height.

Density altitude

The altitude in the standard atmosphere at which air density equals the actual density; increases with high temperature, high elevation and low pressure.

QNH

The altimeter setting that makes the altimeter read aerodrome elevation when on the ground; it is the pressure reduced to mean sea level.

QFE

The altimeter setting that makes the altimeter read zero on the aerodrome reference point; it indicates height above the aerodrome.

Dew point

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

Relative humidity

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

Environmental lapse rate

The actual rate at which temperature decreases with height in the atmosphere; compared with adiabatic rates to determine stability.

Conditional instability

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

Cumulonimbus

A deep convective cloud with a base in the low or middle levels and tops often above 30,000 ft, producing thunderstorms, hail, icing and severe turbulence.

Nimbostratus

A thick, grey, layered cloud producing continuous moderate to heavy precipitation, typically associated with warm fronts and stable air.

Freezing rain

Precipitation that falls as liquid through a warm layer aloft and freezes on contact with a sub-freezing surface, producing severe clear icing.

Radiation fog

Fog formed by radiational cooling of the surface on clear, calm nights, most common in autumn and winter and usually dissipating after sunrise.

Advection fog

Fog formed when warm, moist air moves over a colder surface; it can persist day and night and is common over coastal waters.

Runway visual range

The distance a pilot can see along the runway, reported separately from general visibility and used for low-visibility operations.

Cold front

The boundary where a cold air mass advances and undercuts warm air, producing a narrow band of cumuliform cloud, showers and a sharp wind veer.

Warm front

The boundary where a warm air mass advances over cooler air, producing a broad band of stratiform cloud and steady precipitation ahead of the surface front.

Occluded front

A front formed when a cold front catches up with a warm front, lifting the warm sector off the surface and producing complex frontal weather.

Isobar

A line on a synoptic chart joining points of equal mean sea-level pressure; closely spaced isobars indicate a strong pressure gradient and strong wind.

Anticyclone

A high-pressure system with subsiding air, generally clear skies and light winds, rotating clockwise in the Northern Hemisphere.

SIGMET

A warning of significant weather such as severe turbulence, icing, volcanic ash or tropical cyclones that may affect aircraft safety.

Gradient wind

The theoretical wind blowing parallel to straight isobars, balancing pressure-gradient force and Coriolis force; it is used as a reference for actual wind.

Sea breeze

A local wind blowing from sea to land by day, driven by differential heating of land and water, often reaching 15-20 kt in coastal areas.

Jet stream

A fast, narrow upper-level current near the tropopause, associated with strong wind shear and clear air turbulence.

Microburst

An intense, localized downdraft with a diameter of about 4 km or less, producing severe headwind-to-tailwind shear on final approach.

Clear air turbulence

Turbulence in the upper troposphere, often near jet streams and strong wind shear, occurring without visible cloud.

Thunderstorm mature stage

The stage with both updrafts and downdrafts, producing the most severe weather including hail, lightning, turbulence and heavy rain.

Clear ice

A heavy, hard, irregular ice deposit formed by large supercooled droplets freezing slowly and spreading over the airframe; the most dangerous icing type.

Mountain wave

A wave formed when stable air crosses a mountain barrier with wind increasing with height, producing severe turbulence and lenticular clouds downwind.

Tropical cyclone

A warm-core low-pressure system over tropical oceans with organized convection and maximum sustained winds of 34 kt or more.

TAF

An aerodrome forecast valid for 9-30 hours, using BECMG, TEMPO and FM change groups to indicate expected changes in conditions.