CH 21 Arctic weather

Vocabulary flashcards covering fundamental aviation weather concepts, atmospheric theory, and weather reporting products based on the Aviation Weather Handbook.

Air Parcel

An imaginary volume of air to which properties of atmospheric air may be assigned, used as a tool to describe atmospheric processes.

Standard Atmosphere

A hypothetical vertical distribution of atmospheric temperature, pressure, and density used for pressure altimeter calibrations and aircraft performance calculations.

Troposphere

The layer of the atmosphere extending from the Earth's surface to about $11\,km$ ($36,000\,ft$) where almost all weather occurs.

Tropopause

The transition boundary between the troposphere and the stratosphere.

Lapse Rate

The rate of decrease in an atmospheric variable (usually temperature) with an increase in altitude.

Temperature Inversion

An atmospheric layer in which the temperature increases with altitude, often resulting in high stability and little turbulence.

Radiation

The transfer of heat energy through space by electromagnetic waves.

Conduction

The transfer of energy by molecular activity from one substance to another in contact with, or through, a substance.

Convection

The transport of heat within a fluid via motions of the fluid itself, playing a vital role in atmospheric heat transfer.

Specific Heat Capacity

The measure of heat energy required to increase the temperature of a unit quantity of a substance by a certain temperature interval.

Hydrologic Cycle

The continuous circulation of water in the Earth-atmosphere system including evaporation, transpiration, condensation, and precipitation.

Relative Humidity

The ratio (expressed as a percentage) of water vapor actually in the air compared to the amount it could hold at a specific temperature and pressure.

Dewpoint

The temperature an air parcel must be cooled at constant pressure to allow the water vapor in the parcel to condense into water.

Latent Heat

The quantity of heat energy released or absorbed by a unit mass of a substance when it undergoes a phase transition.

Greenhouse Effect

The heating effect resulting from the atmosphere absorbing infrared radiation trying to escape from the Earth back to space.

Diurnal Temperature Variation

The daytime maximum and nighttime minimum of air temperature caused by the Earth's rotation.

Atmospheric Pressure

The force per unit area exerted by the weight of the atmosphere.

Density Altitude

Pressure altitude corrected for temperature deviations from the standard atmosphere; an index to aircraft performance.

Hadley Cell

Low-latitude air movement toward the Equator that rises vertically with poleward movement in the upper atmosphere.

Jet Stream

Relatively narrow bands of strong wind in the upper levels of the atmosphere blooming generally from west to east.

Pressure Gradient Force (PGF)

The force created by pressure differences that drives wind from higher pressure to lower pressure.

Coriolis Force

An apparent force that deflects moving objects to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

Sea Breeze

A coastal local wind that blows from sea to land caused by temperature differences when the sea surface is colder than the land.

Wind Shear

The sudden, drastic change in wind speed and/or direction over a small area.

Air Mass

A large body of air with generally uniform temperature and humidity.

Front

A boundary or transition zone between two different air masses.

Dryline

A low-level boundary separating moist and dry air masses, typically found in the southern and central High Plains of the U.S.

Adiabatic Process

A process in which no heat transfer occurs into or out of a parcel of air as it ascends or descends.

Lifted Condensation Level (LCL)

The level at which a parcel of moist air lifted dry adiabatically becomes saturated, marking the base of clouds.

Atmospheric Stability

The property of ambient air that either enhances or suppresses vertical motion of air parcels.

Convective Available Potential Energy (CAPE)

The maximum amount of energy available to an ascending air parcel for convection, measured in $J/kg$.

Collision-Coalescence

The growth process where cloud droplets collide and stick together to form larger drops, eventually falling as rain.

WSR-88D (NEXRAD)

The Weather Surveillance Radar (1988 Doppler) used by the NWS to detect precipitation and atmospheric targets.

Mountain Wave

An atmospheric disturbance that develops as air masses interact with mountainous terrain, potentially causing severe turbulence.

Intertropical Convergence Zone (ITCZ)

The zone near the equator where the northeast and southeast trade winds converge and air rises.

Mist (BR)

A visible aggregate of water droplets or ice crystals that reduces visibility to between $5/8\,sm$ and $7\,sm$.

METAR

Aviation Routine Weather Report; the primary code format for reporting surface meteorological data.

PIREP

Pilot Weather Report; an observation of in-flight weather conditions reported by a pilot.

SIGMET

Significant Meteorological Information; an advisory concerning specified en route weather phenomena affecting aircraft safety.

AIRMET

Airmen’s Meteorological Information; an advisory for weather phenomena of lower intensities than those requiring SIGMETs.

Terminal Aerodrome Forecast (TAF)

A concise statement of expected meteorological conditions significant to aviation within $5\,sm$ of the center of an airport's runway complex.