DGCA ATPL 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

The ISA sea-level pressure is 1013.25 hPa (29.92 in Hg). It is the reference for pressure altitude and flight levels.

Tropopause definition

The boundary between troposphere and stratosphere where the temperature lapse rate becomes isothermal or inverses. Its height varies from about 8 km at the poles to 16-18 km at the equator.

ISA temperature lapse rate

In the ISA the temperature decreases at 1.98 deg C per 1000 ft (6.5 deg C/km) from sea level up to 11 km (36,090 ft), above which it is constant at -56.5 deg C.

Density altitude

Pressure altitude corrected for temperature deviation from ISA. It is the altitude at which the aircraft would perform as if in ISA conditions, and high values reduce performance.

Ideal gas law

p = rho R T, where p is pressure, rho is density, R is the gas constant and T is absolute temperature. Density is proportional to pressure and inversely proportional to temperature.

QNH

The altimeter subscale setting that makes the altimeter indicate elevation above mean sea level at the aerodrome when the aircraft is on the ground.

QFE

The altimeter subscale setting that makes the altimeter indicate height above the aerodrome reference point (usually the runway threshold) when on the ground.

Transition altitude

The altitude at or below which the altimeter is set to QNH. Above it, the altimeter is set to standard pressure 1013.25 hPa and flight levels are used.

Dew point

The temperature to which air must be cooled at constant pressure to become saturated. The dew point depression is the difference between temperature and dew point.

Dry adiabatic lapse rate

The rate at which unsaturated air cools when lifted adiabatically: about 3 deg C per 1000 ft (9.8 deg C/km).

Lifting condensation level

The height at which air lifted dry adiabatically becomes saturated. It can be estimated as 400 ft per deg C of dew point depression.

Conditional instability

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

Radiation fog

Fog formed on clear calm nights when the ground cools by radiation and the air above it is cooled to its dew point. It usually dissipates after sunrise.

Advection fog

Fog formed when warm moist air moves over a cold surface and is cooled to its dew point. It is common over the sea and coasts and can persist for days.

Cumulonimbus cloud

A deep convective cloud with strong up- and downdraughts, severe turbulence, icing, hail and lightning. It produces showers and gust fronts.

Cold front

The boundary where cold air advances under warm air. It has a steep slope, a narrow band of heavy showers and squalls, and clearing behind.

Warm front

The boundary where warm air rides over cold air. It has a shallow slope, a wide band of layered cloud and continuous rain ahead, and warming after passage.

Occluded front

A front formed when a cold front overtakes a warm front and lifts the warm air off the ground. Its weather depends on whether it is a cold or warm occlusion.

Indian southwest monsoon

The seasonal wind reversal from June to September that brings moist onshore air and heavy rain to India. It is driven by differential heating of land and sea.

Monsoon trough

A low-pressure trough extending across India during the monsoon. Its position determines the distribution of monsoon rainfall and break conditions.

Tropical cyclone formation

Tropical cyclones form over warm oceans (SST above about 26.5 deg C) with low vertical wind shear. They do not form within about 5 degrees of the equator.

Microburst

A small-scale downdraught (less than about 4 km across) that produces a sudden headwind-to-tailwind shear near the ground. It is a major hazard on approach and departure.

Clear air turbulence

Turbulence in clear air, often associated with jet streams near the tropopause and on the anticyclonic side of the jet. It is not visible on radar.

Freezing rain

Supercooled water drops that freeze on impact with the airframe. It produces the most rapid and dangerous clear ice accumulation and is associated with warm fronts aloft.

METAR

A routine aerodrome weather report issued hourly or half-hourly. It includes wind, visibility, weather, cloud, temperature, dew point and QNH.

TAF

A terminal aerodrome forecast valid for a specified period (typically 9, 24 or 30 hours). It uses BECMG, TEMPO and FM change groups.

SIGMET

A warning of significant weather (thunderstorms, icing, turbulence, volcanic ash, tropical cyclones) affecting the safety of aircraft within a flight information region.

AIRMET

A warning of moderate hazards (moderate icing, turbulence, mountain obscuration, low-level wind shear) affecting low-level flights within a flight information region.

CAVOK

A METAR/TAF code meaning visibility 10 km or more, no cloud below 5000 ft or below the highest minimum sector altitude, and no cumulonimbus or towering cumulus.

Volcanic ash advisory

A warning issued by a Volcanic Ash Advisory Centre giving the position and forecast movement of volcanic ash clouds. Ash can damage engines and windscreens.

Jet stream

A strong narrow band of wind near the tropopause. The polar front jet and subtropical jet are the main types and are associated with CAT and depressions.

El Nino

A warming of the central and eastern tropical Pacific that affects global weather. It is associated with weaker Indian monsoon rainfall in many years.