ABSOLUTE INSTABILITY.—The state ofa column of air in the atmosphere when it has a superadiabatic lapse rate of temperature. An air parcel displaced vertically would be accelerated in the direction of the displacement.
ABSOLUTE STABILITY.—The state of acolumn of air in the atmosphere when its lapse rate of temperature is less than the saturation adiabatic lapse rate. An air parcel will be more dense than its environment and tend to sink back to its level of origin.
ABSOLUTE VORTICITY.—The vorticity ofa fluid particle determined by taking into account Earth’s movement.
ABSORPTION.—The process in whichincident radiant energy is retained by a substance.
ADVECTION.—The horizontal transport ofan atmospheric property solely by the mass mo-tion (velocity field) of the atmosphere.
ADVECTION FOG.—Fog caused by theadvection of moist air over a cold surface, and the consequent cooling of that air to below its dew point.
AIR MASS.—A widespread body of air thatis approximately homogeneous in its horizontal extent, with reference to temperature and moisture.
ALBEDO.—The ratio of the amount of electromagneticradiation reflected by a body to the amount incident upon it.
ANABATIC WIND.—An upslope wind;usually applied only when the wind is blowing up a hill or mountain as the result of surface heating.
ANTARCTIC FRONT.—The semiperma-nent,semicontinuous front between the antarc-tic air of the Antarctic Continent and the polar air of the southern oceans; generally comparable to the arctic front of the Northern Hemisphere.
ANTICYCLOGENESIS.—The strengtheningor development of an anticyclonic circulation in the atmosphere.
ANTICYCLOLYSIS.—The weakening of ananticyclonic circulation in the atmosphere.
ANTICYCLONE.—A closed circulation inthe atmosphere that has a clockwise rotation in the Northern Hemisphere and a counterclockwise rotation in the Southern Hemisphere. Used inter-changeably with high.
ANTICYCLONIC.—Refers to the rotationpattern of anticyclones. See ANTICYCLONE.
ARCTIC FRONT.—The semipermanent,semicontinuous front between the deep, cold arc-tic air and the shallower, basically-less-cold polar air of northern latitudes; generally comparable to the antarctic front of the Southern Hemisphere.
AUTOCONVECTIVE LAPSE RATE.—Thetemperature lapse rate in an atmosphere where density is constant with height.
BACKING.—A change in wind direction ina counterclockwise manner in the Northern Hemisphere and a clockwise manner in the Southern Hemisphere.
BLOCKING HIGH.—An anticyclone that re-mainsstationary or moves slowly westward so as to effectively block the movement of migratory cyclones across its latitudes.
BRIGHT BAND.—As seen on a range-heightindicator, the enhanced radar echo of snow as it melts to rain. The freezing level can normally be found approximately 1,000 feet above this band.
BUYS BALLOT’S LAW.—The law describ-ingthe relationship of horizontal wind direction to pressure: In the Northern Hemisphere, with your back to the wind, the lowest pressure will be to your left; in the Southern Hemisphere, the reverse is true.
CENTER OF ACTION.—Any one of thesemipermanent high- or low-pressure systems.
CENTRAL PRESSURE.—The atmosphericpressure at the center of a high or low; the highest pressure in a high, the lowest in a low.
CHROMOSPHERE.—A thin layer ofrelatively transparent gases above the photosphere of the Sun.
CLOSED HIGH.—A high that is completelyencircled by an isobar or contour line.
CLOSED LOW.—A low that is completelyencircled by an isobar or contour line.
COLD-CORE HIGH.—Any high that isgenerally characterized by colder air near its center than around its periphery at a given level in the atmosphere.
COLD-CORE LOW.—Any low that isgenerally characterized by colder air near its center than around its periphery at a given level in the atmosphere.
CONDENSATION.—The physical process bywhich a vapor becomes a liquid or solid.
CONDITIONAL INSTABILITY.—The stateof a column of air in the atmosphere when its temperature lapse rate is less than the dry adiabatic lapse rate but greater than the satura-tion adiabatic lapse rate.
CONTOURS.—Term referring to constantheight lines on a constant-pressure chart. Used in-terchangeably with isoheights. Each line represents a line of constant elevation above a cer-tain reference level (usually mean sea level).
CONVECTION.—Atmospheric motions thatare predominantly vertical, resulting in the ver-tical transport and mixing of atmospheric properties.
CORONA.—(1) A set of one or moreprismatically colored rings of small radii, concen-trically surrounding the disk of the Sun, Moon, or other luminary when veiled by a thin cloud.
A corona maybe distinguished from the relativelycommon 22° halo by its color sequence, which is from blue inside to red outside, the reverse of that of the 22° halo. Coronas are produced by diffraction and reflection of light from water droplets. (2) The pearly outer envelope of the Sun.
COUNTERRADIATION.—(also called backradiation) The downward flow of atmospheric radiation passing through a given level surface, usually taken as Earth’s surface. It is the prin-cipal factor in the GREENHOUSE EFFECT.
CUT-OFF HIGH.—A warm high displacedand lying poleward of the basic westerly current.
CUT-OFF LOW.—A cold low displaced andlying equatorward of the basic westerly current.
CYCLOGENESIS.—Any development orstrengthening of cyclonic circulation in the atmosphere. The initial appearance of a low or trough, as well as the intensification of an existing cyclonic flow.
CYCLOLYSIS.—Any weakening of cycloniccirculation in the atmosphere.
CYCLONIC.—A counterclockwise rotationin the Northern Hemisphere and a clockwise rota-tion in the Southern Hemisphere.