T

Tail doppler radar - A scanning Doppler radar mounted in the tail of an airplane, usually employed for helical scanning.

Teardrop balloon- A sounding balloon that, when operationally inflated, resembles an inverted teardrop.

Telephotometer- A photometer that measures the amount of light received from a distant light source. When specifically used to measure the transmissivity of the intervening atmosphere (or other medium), it is usually termed a transmissometer.

Telethermometer- A temperature-measuring system in which the thermally sensitive element is located at a distance from the indicating element.

Telethermoscope - A temperature telemeter, frequently used in a weather station to indicate the temperature at the instrument shelter located outside.

Television and Infrared Observation Satellite- The first satellite series dedicated to meteorological observations. TIROS-1, launched in April 1960, carried a vidicon television camera to provide visible images of the earth. TIROS-8, launched in December 1963, introduced APT, while TIROS-9, launched in January 1965 in a sun-synchronous orbit, produced the first global composite imagery. The first ten satellites in the TIROS series, launched from 1960 to 1965, were experimental systems. From 1966 to 1969 TIROS satellites were used for the first series of operational polar-orbiting satellites, the TIROS Operational System. These satellites were named ESSA-1 through ESSA-9. A second series of operational satellites, the Improved TIROS Operational System, was launched between 1970 and 1976 and includes the ITOS-1 satellite, as well as NOAA-1 through 5. The current polar-orbiting series began with TIROS-N, launched on 13 October 1978, and continuing with NOAA-6, -7, and -12. NOAA-8 through -11 and NOAA-14 were modified versions of TIROS- N, designated Advanced TIROS-N satellites. Like GOES, the polar-orbiting satellites are typically given a letter designation as they are built and then renamed with a number after they are successfully launched. Thus NOAA-J became NOAA-14 after launch. TIROS-N is an exception to this rule.

Temperature Humidity Infrared Radiometer- A two-channel (6.5 and 11.5 ?m) scanning radiometer flown on Nimbus- 4 through -7 used to provide information on moisture and high-level clouds in the upper troposphere and stratosphere.

Terminal Doppler Weather Radar- Doppler radar installed during the 1990s by the Federal Aviation Administration at U.S. airports with high traffic density or susceptibility to wind shear.

Tethered balloon- A positively buoyant unmanned balloon attached to a cable that is used to raise and lower the balloon. Instrument packages are suspended from the balloon to measure characteristics such as air temperature, winds, humidity, refractive index, trace gases, and aerosols as functions of time (by keeping the height constant) or height (by raising and lowering the balloon). They have been used for measuring both mean values and turbulent fluctuations. Balloon heights of over a kilometer have been reached, and instrument packages are sometimes deployed at more than one height below the balloon. Tethered balloons have been deployed from fixed locations over land and from ships.

Tethersonde- A radiosonde attached to a fixed or tethered balloon. The balloon is usually larger than a balloon used for upper-air soundings, and the tether usually limits the sounding to the boundary layer. The radiosonde is typically moved up and down the tether to get multiple, high-resolution profiles of the boundary layer.

Tetroon- A balloon of tetrahedron shape made from a cylinder of plastic film. The cylinder is sealed orthogonally at the two ends, producing a low-cost balloon that simulates a sphere.

Thematic mapper- A seven-channel instrument on Landsat series satellites used to make maps of infrared emission and reflection from the earth. Most thematic mapper images are used to study vegetation, geology, and other surface features.

Theodolite - An optical instrument, similar to a surveyor's transit telescope, used to visually track a radiosonde balloon and determine its azimuth and elevation angles while in flight.

Thermistor- A device with electrical resistance that varies markedly and monotonically and that possesses a negative temperature coefficient of resistivity.

Thermistor thermometer- A device for estimating temperature based on a known relationship of its electrical resistance to temperature.

Thermocouple- A temperature-sensing element that converts thermal energy directly into electrical energy.

Thermocouple thermometer- (Also called thermoelectric thermometer.) A type of electrical thermometer consisting of two thermocouples that are series connected with a potentiometer and a constant-temperature bath.

Thermoelectric thermometer- (Also called thermocouple thermometer.) A type of electrical thermometer consisting of two thermocouples that are series connected with a potentiometer and a constant-temperature bath.

Thermograph- A self-recording thermometer.

Thermohygrograph- A recording instrument combining, on one record, the variation of atmospheric temperature and humidity content as a function of time. The most common hygrothermograph is a hair hygrograph combined with a thermograph.

Thermohygrometer- An instrument that measures both atmospheric water vapor content and temperature.

Thermo integrator- An apparatus, used in studying soil temperatures, for measuring the total supply of heat during a given period. It consists of a long nickel coil forming a 100-ohm resistance thermometer and a 6-volt battery, the current used being recorded on a galvanometer. The coil is attached to a rod for insertion. A mercury thermometer can be used. The instrument can also measure the heat balance in a plant cover.

Thermometer - An instrument for measuring temperature by utilizing the variation of the physical properties of substances according to their thermal states.

Thermometer screen- (Also called thermoscreen, thermometer shelter, instrument shelter.) A boxlike structure designed to protect thermometers from exposure to direct sunshine while at the same time providing adequate ventilation.

Thermometer shelter- (Also called thermoscreen, thermometer screen, instrument shelter.) A boxlike structure designed to protect thermometers from exposure to direct sunshine while at the same time providing adequate ventilation.

Thermometer support- A device used to hold liquid-in-glass maximum and minimum thermometers in the proper recording position inside an instrument shelter, and to permit them to be read and reset.

Thermopile - A transducer for converting thermal energy directly into electrical energy. It is composed of pairs of thermocouples that are connected either in series or in parallel. The output voltage of N pairs of series-connected thermocouples is N times the voltage developed by a single pair, while the current developed by N pairs of parallel connected thermocouples is N times the current developed by a single pair. Thermopiles are used in thermoelectric radiation instruments when the output of a single pair of thermocouples is not large enough.

Thermoscope - An instrument that measures temperature changes, in contrast with a thermometer, which measures the absolute temperature.

Thermoscreen - (Also called thermometer shelter, thermometer screen, instrument shelter.) A boxlike structure designed to protect thermometers from exposure to direct sunshine while at the same time providing adequate ventilation.

Thrust anemometer- An anemometer that measures the wind velocity by sensing the drag force on an object, commonly a cylinder or sphere, placed in the flow.

Tide gauge- A device for measuring the height of tide.

Time height indicator - A type of radar display on which the reflectivity, Doppler velocity, or other properties of echoes are displayed as a function of time and height in rectangular coordinates.

Tipping bucket rain gauge - A recording rain gauge in which the water collected continuously drains through a funnel into one of a pair of chambers or buckets that are balanced bistably on a horizontal axis.

TIROS-N Operational Vertical Sounder - An atmospheric sounding system composed of three instruments carried on the TIROS-N and NOAA-6 through -14 polar-orbiting satellites.

TOPEX;Ocean Topography Experiment - The TOPEX/Poseidon satellite, launched in September 1992, uses sophisticated altimeters to make sea level measurements in combination with a microwave radiometer to correct the altimeter measurements for changes in total water vapor content of the atmosphere, resulting in an absolute accuracy of about 4 cm.

Topside sounder- A satellite designed to determine ion concentration within the ionosphere as measured from above the ionosphere.

Torricelli's tube- An early and once universal name for the mercury barometer.

Torricellian vacuum - The “vacuum” above the column in a mercury barometer.

Torsion hygrometer- A hygrometer in which the rotation of the hygrometric element is a function of the humidity.

Total Ozone Mapping Spectrometer - A satellite instrument that measures backscattered ultraviolet radiation to infer total column ozone.

Total Ozone Monitoring Satellite- Satellite-borne spectrometer for measuring the total column amount of ozone above the earth. The spectrometer works by measuring the amount of ultraviolet radiation scattered back into space at several wavelengths. Data from TOMS have been invaluable in evaluating long-term trends in global ozone and also annual events such as the Antarctic ozone hole.

Totalizer rain gauge - A nonrecording rain gauge designed to be used at stations that can be visited only infrequently.

Trace recorder- (Also called ombrometer, micropluviometer, trace recorder.) A rain gauge capable of measuring very small amounts of precipitation.

Tracking radar- A radar that is primarily used to automatically track the position of nonmeteorological targets that are usually small relative to the radar pulse volume, for example, an aircraft or balloon.

Transducer- A device for converting energy from one form to another.

Transmissometer- (Also called telephotometer; transmittance meter, hazemeter.) An instrument for measuring the extinction coefficient of the atmosphere and for the determination of visual range.

Transmit receive tube- A gas-filled waveguide cavity that acts as a short circuit when ionized by high-power energy but is transparent to low-power emission when not ionized. It is used as a switch to protect the receiver of a radar from the high power of the transmitter while passing the low-power signals received at the antenna. "