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Air masses are classified according to their source regions. Four such regions are generally recognized- (1) equatorial (E), the doldrum area between the north and south trades; (2) tropical (T), the trade wind and lower temperate regions, (3) polar (P), the higher temperate latitudes; and (4) Arctic or Antarctic (A), the north or south polar regions of ice and snow. This classification is a general indication of relative temperature, as well as latitude of origin. Air masses are further classified as maritime (m) or continental (c), depending upon whether they form over water or land. This classification is an indication of the relative moisture content of the air mass. A third classification sometimes applied to tropical and polar air masses indicates whether the air mass is warm (w) or cold (k) relative to the underlying surface. The w and k classifications are primarily indications of stability, cold air being more stable.

Related Terms

FLASH POINT

The lowest temperature at which a liquid gives off sufficient vapor to form a flammable mixture with air near the surface of the liquid. The flashpoint temperature is determined by laboratory testing in a prescribed apparatus.

Establishes the danger point when transferring, pumping, and firing procedures are concerned.

PHOTOECOLOGY

The application of air photography to ecology, integrated land resource studies, and forestry.

PERMISSIBLE EXPOSURE LIMIT

The level of air contaminants that represents an acceptable exposure level as specified in standards set by a national government agency; generally expressed as 8-hour time-weighted average concentrations. Abbreviated PEL.

PERCUSSION DRILL

A drilling machine usually using compressed air to drive a piston that delivers a series of impacts to the shank end of a drill rod or steel and attached bit.

PACHUCA TANK

Air-agitated, solidliquid mixing vessel in which the air is injected into the bottom of a center draft tube; air and solids rise through the tube, with solids exiting the top of the tube and falling through the bulk of the liquid.

OPEN-CYCLE GAS TURBINE

A gas turbine prime mover in which air is compressed in the compressor element, fuel is injected and burned in the combustor, and the hot products are expanded in the turbine element and exhausted to the atmosphere.

NUTATOR

A mechanical or electrical device used to move a radar beam in a circular, conical, spiral, or other manner periodically to obtain greater air surveillance than could be obtained with a stationary beam.

NOZZLE-MIX GAS BURNER

Aburnerinwhich injection nozzles mix air and fuel gas at the 374 burner tile. nozzle throat with the

NEEDLE BLOW

A blow-molding technique in which air is injected into the plastic article through a hollow needle inserted in the parison.

NATURAL-DRAFT COOLING TOWER

A cooling tower that depends upon natural convection of air flowing upward and in contact with the water to be cooled.

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