Aeronautical Terms beginning with T
True altitude
The exact distance above mean sea level.
Target
In radar, any of the many types of objects detected by radar.
Temperature
In general, the degree of hotness or coldness as measured on some definite temperature scale by means of any of various types of thermometers.
Temperature inversion
Inversion. An increase in temperature with height-a reversal of the normal decrease with height in the troposphere; may also be applied to other meteorological properties.
Terrestrial radiation
The total infrared radiation emitted by the Earth and its atmosphere.
Thermograph
A continuous-recording thermometer.
Thermometer
An instrument for measuring temperature.
Theodolite
An optical instrument which, in meteorology, is used principally to observe the motion of a pilot balloon.
Thunderstorm
In general, a local storm invariably produced by a cumulonimbus cloud, and always accompanied by lightning and thunder.
Tornado (sometimes called cyclone, twister)
A violently rotating column of air, pendant from a cumulonimbus cloud, and nearly always observable as “funnel-shaped.” It is the most destructive of all small-scale atmospheric phenomena.
Towering cumulus
A rapidly growing cumulus in which height exceeds width.
Tower visibility
Prevailing VIsibility determined from the control tower.
Trade winds
Prevailing, almost continuous winds blowing with an easterly component from the subtropical high pressure belts toward the intertropical convergence cone; northeast in the Northern Hemisphere, southeast in the Southern Hemisphere.
Transmissometer
An instrument system which shows the transmissivity of light through the atmosphere. Transmissivity may be translated either automatically or manually into visibility and/or runway visual range.
Tropical air
An air mass with characteristics developed over low latitudes. Maritime tropical air (mT), the principal type, is produced over the tropical and subtropical seas; very warm and humid. Continental tropical (cT) is produced over subtropical arid regions and is hot and very dry. Compare polar air.
Tropical cyclone
A general term for a cyclone that originates over tropical oceans. By international agreement, tropical cyclones have been classified according to their intensity, as follows: (1) tropical depression-winds up to 34 knots (64 km/h); (2) tropical storm-winds of 35 to 64 knots (65 to 119 km/h); (3) hurricane or typhoon-winds of 65 knots or higher (120 km/h).
Tropical depression
A cyclone that originates over tropical oceans. A tropical depression winds up to 34 knots (64 km/h).
Tropical storm
A cyclone that originates over tropical oceans. A tropical storm has winds of 35 to 64 knots (65 to 119 km/h).
Tropopause
The transition zone between the troposphere and stratosphere, usually characterized by an abrupt change of lapse rate.
Troposphere
That portion of the atmosphere from the earth’s surface to the tropopause; that is, the lowest 10 to 20 kilometers of the atmosphere. The troposphere is characterized by decreasing temperature with height. and by appreciable water vapor.
Trough (also called trough line)
In meteorology, an elongated area of relatively low atmospheric pressure; usually associated with and most clearly identified as an area of maximum cyclonic curvature of the wind flow (isobars, contours, or streamlines); compare with ridge.
True wind direction
The direction, with respect to true north, from which the wind is blowing.
Turbulence
In meteorology, any irregular or disturbed flow in the atmosphere.
Twilight
The intervals of incomplete darkness following sunset and preceding sunrise. The time at which evening twilight ends or morning twilight begins is determined by arbitrary convention, and several kinds of twilight have been defined and used; most commonly civil, nautical, and astronomical twilight.
Twister
In the United States, a colloquial term for tornado.
Typhoon
A tropical cyclone in the Eastern Hemisphere with winds in excess of 65 knots (120 km/h).
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