Tcu: An abbreviation sometimes used to denote a towering cumulus cloud (cumulus congestus). Manually appended when appropriate to the lowest cloud layer in a METAR report for ASOS.

Teleconnection: A linkage between different meteorological features separated by great distances. For example, statistics show that the rainfall in the southern Sahara (Sahel) varies with the phase of the El Niño Southern Oscillation (ENSO) in the Pacific.

Temperature: The degree of hotness or coldness of substance as measured by a thermometer. It is also a measure of the average speed or kinetic energy of the atoms and molecules in a substance.

Temperature Humidity Index (THI): A well-known and often used guide to human comfort or discomfort based on the conditions of temperature and relative humidity. See my FAQ page to view an actual guide!

Temperature Inversion: An increase in air temperature with height.

Temperature Scales: (a) Celsius (C) previously called Centigrade, has the freezing point of water at 0°C and the boiling point at 100°C; (b) Fahrenheit (F) has the freezing point of pure water at 32°F and the boiling point at 212°F; (c) Kelvin (K) also known as the absolute temperature, has zero at the lowest possible temperature (-273.15°C) and boiling point at 373.15°C. The degree sign (°) is NOT used when writing temperatures in Kelvin. e.g. 8°K is wrong! 8K is the correct form.
Conversion formulae:
F = (C x 9/5) + 32
C = (F-32) x 5/9
K = C + 273.15

Tendency (in meteorology): The rate of change of an element, mostly used for the change of barometric pressure over a period of three hours.

Tephigram: An aerological diagram with the x, y coordinates temperature (T) and Entropy (phi). The lines of equal entropy are also the dry adiabatics. It is used for plotting temperature and humidity at specified pressure levels. Stability can be worked out by comparing the plotted lapse rate with the lines representing dry and wet adiabatics.

Thermal: A volume of air which rises because it is warmer (less dense) than its environment. Many thermals form when the air near the surface is warmed by contact with ground heated by the sun.

Thermal Belts: Horizontal zones of vegetation found along hillsides that are primarily the result of vertical temperature variations.

Thermal Circulations: Air flow resulting primarily from the heating and cooling of air.

Thermal Lows and Thermal Highs: Areas of low and high pressure that are shallow in vertical extent and are produced primarily by surface temperatures.

Thermal Tides: Atmospheric pressure variations due to the uneven heating of the atmosphere by the sun.

Thermal Wind: The geostrophic wind shear between the base and top of a deep layer, often chosen to be from 1,000 to 500 mbar. It depends on the horizontal temperature gradient; in the northern hemisphere, the thermal wind blows so that low temperatures lie on the left-hand side.

Thermistor: An electrical resistance device used in the measurement of temperature.

Thermocouple: An electric thermometer consisting of a conductor whose resistance to the flow of current is temperature-dependent; commonly used in radiosondes.

Thermodynamic Diagram: Another name for an aerological diagram.

Thermodynamics: This deals with the transfer of heat into energy and energy into heat.

Thermograph: An instrument that measures and records air temperature.

Thermometer: An instrument for measuring temperature. The most common are liquid-in-glass, which have a sealed glass tube attached to a glass bulb filled with liquid.

Thermometer Screen: A housing which shields the instruments from sunlight or radiation from the ground but allows air to pass through. The thermometer bulbs are generally 4 feet above the ground.

Thermosphere: The atmospheric layer above the mesosphere (above about 85km) where the temperature increases rapidly with height.

Thickness: The term used for the depth of a layer of air (often the layer between 1,000 and 500 mbar). The thickness varies with the temperature: warm air expands so its thickness is greater than for colder, denser column.

Thunder: The sound caused by the shock wave from a narrow channel of air heated by lightning to around 28,000°C!

Thunderstorm: Rain, hail or snow shower accompanied by flashes of lightning from a Cb cloud.

Tipping-Bucket Gauge: A recording rain gauge consisting of two compartments ("buckets"), each capable of holding 0.025cm of water. When one compartment fills, it tips and the other compartment takes its place.

TIPPS: see Trans-Ionospheric Pulse Pairs

Tornado: A destructive vortex formed by extremely rapid rotation of air in and below the base of a Cb. The rate of spin reduces air pressure and causes condensation to form a funnel-shaped cloud extending down to the ground. Rotational speed may reach 300 knots, enough to destroy buildings along its track which may be less than 100 yards wide but can extend to a mile. Wide tornadoes sometimes contain several smaller 'suction vortices' rotating around the center. In the tiny town of Codell, Kansas, tornadoes hit on three consecutive years--1916, 1917, 1918--and each time on the SAME date: May 20! Though on a much smaller scale (F0 and maybe F1), Los Angeles and surrounding area has experienced more tornadoes than the Kansas City area over the past 20 years! Tornadoes once fought for this country too!....... During the War of 1812, more British troops were killed or injured by a monstrous tornado that roared through Washington D.C., than from all the firepower the American troops could muster trying to defend the city.

Tornado Outbreak: A series of tornadoes that forms within a particular region--a region that may include several states. Often associated with widespread damage and destruction.

Tornado Warning: A warning issued when a tornado has actually been observed either visually or on a radar screen. It is also issued when the formation of tornadoes is imminent.

Tornado Watch: A forecast issued to alert the public that tornadoes may develop within a specified area.

Torro Index: A scale of tornado intensity.

Towering: A mirage in which the size of an object is magnified.

Towering Thunderheads: Extremely tall cumulus clouds whose tops reach the boundary between the troposphere and the stratosphere (tropopause). Created by the surface heating of Earth which results in powerful convection currents. Capable of producing thunderstorms, hence the name. They tend to look like the mushroom clouds created from nuclear blasts over and under water.

Strong convection currents caused by the heated land make these thunderheads

Trace (of precipitation): An amount of precipitation less than 0.01 inch (0.025cm). Even if no water is visible on the end of the dipstick used in a standard rain gauge, but precipitation was observed, no matter how brief, trace should be recorded.

Trade Winds: Winds with a predominantly easterly component which spread out from the subtropical anticyclones towards the equator.

Trade Wind Inversion: A temperature inversion frequently found in the subtropics over the eastern portions of the tropical oceans.

Trans-Ionospheric Pulse Pairs (TIPPs): TIPPs consist of 2 sharp bursts of energy a few tens of millionths of a second apart. The second pulse in a TIPP is a reflection off Earth's surface, which means the discharge must have occurred at sufficient height in the atmosphere to have originated within clouds. Los Alamos' ALEXIS satellite (whose primary function was to detect clandestine nuclear weapon detonations) produced the first scientific reports of TIPPs in 1994. Evidence concludes that TIPPs arise from energetic lightning discharges.

Translucidus: A translucent patch, sheet, or layer of clouds through which the Sun or Moon can be seen. Applies to altocumulus, altostratus, stratocumulus, and stratus.

Transpiration: The process by which water in plants is transferred as water vapor to the atmosphere.

Trajectory: The path followed by an object (in meteorology usually a mass of air, e.g. the path of a depression).

Translucidus (tr.): Thin layer clouds through which the sun can be seen.

Tropical Air: A very warm air mass originating in subtropical anticyclones near latitude 30 degrees. It can be very moist after a long sea passage (Maritime Tropical). If it comes mostly overland it is Continental Tropical and gives very high temperatures in summer.

Tropic of Cancer: The parallel of latitude, 23.5°N latitude, marking the northern limit of the Sun's vertical rays.

Tropic of Capricorn: The parallel of latitude, 23.5°S latitude, marking the southern limit of the Sun's vertical rays.

Tropical (T) Air Mass: A warm-to-hot air mass that forms in the subtropics.

Tropical Cyclone: A vigorous depression in tropical latitudes producing winds of gale or hurricane force. Similar systems are called Hurricanes in the West Indies and the USA but Typhoons in the China Sea and western Pacific. I think they call them Willy Willies or something like that near Australia.

Tropical Depression: A mass of thunderstorms and clouds generally with a cyclonic wind circulation of between 20 and 34 knots.

Tropical Disturbance: An organized mass of thunderstorms with a slight cyclonic wind circulation of less than 20 knots.

Tropical Easterly Jet: A jet stream that forms on the equatorward side of the subtropical highs near 15km asl (above mean sea level).

Tropical Monsoon Climate: A tropical climate with a brief dry period of perhaps one or two months.

Tropical Rain Forest: A type of forest consisting mainly of lofty trees and a dense undergrowth near the ground. NOT THE SAME AS A JUNGLE! Tarzan cartoons depict our hero swinging on vines in a rain forest! :) See Jungle for definition of jungle.

Tropical Storm: Organized thunderstorms with a cyclonic wind circulation between 35 and 64 knots.

Tropical wet-and-dry climate: A tropical climate poleward of the tropical wet climate where a distinct dry season occurs, often lasting for two months or more. It is transitional between the wet tropics and the subtropical steppes.

Tropical Wet Climate: A tropical climate with sufficient rainfall to produce a dense tropical rain forest.

Tropopause: The atmospheric boundary between the troposphere and the stratosphere. It is usually marked by a kink in the temperature profile where the lapse rate changes from about 6.5°C per km to almost isothermal.

Troposphere: The lower layer of the atmosphere where most of the weather takes place. On average, the temperature decreases with height up to the tropopause.

Trough (of low pressure): Appears on weather maps as an extension from a depression.

Trowal: A Canadian term for a trough with warm air aloft. (Rather similar to an Occlusion.)

Tuba (tub.): Also known as Funnel Cloud, and is a column or inverted cone of cloud extending below the base of a Cb indicating a vortex. It may be the first indication of a tornado or waterspout; A cloud column that hangs from a cloud base and, upon reaching Earth's surface, forms a tornado or waterspout. This applies to cumulus and cumulonimbus.

Tundra Climate: Found almost exclusively in the Northern Hemisphere or at high altitudes in many mountainous regions. A treeless climatic realm of sedges, grasses, mosses, and lichens dominated by a long, bitterly cold winter.

Turbulence: Disturbed air motions caused by numerous eddies of different size, making conditions rough for flying.

Twilight: The time at the beginning of the day immediately before sunrise and at the end of the day after sunset when the sky remains illuminated.

Twilight Arc: An arc of yellow to red sunlight, before sunrise or after sunset. The twilight arc is more pronounced when the atmosphere is contaminated with aerosols due to volcanic eruptions. Then, there is much atmospheric scattering, making the arc an intense red, orange and yellow.

Twilight Wedge: The twilight wedge is the dark shadow band of the earth, visible in the east when the sun has just set, or in the west if the sun is nearly rising. During sunset, the shadow band rises quicker than the sun sinks below the horizon and gradually smoothens out with the evening sky, because the observer first sees the shadow edge-on, when the tangent point of the sunlight on the earth is near the observer (i.e. the sun is very near the horizon), and later on, the tangent point through which the edge of the shadow runs has moved westward. For sunrise, the sequence is reversed. Often, one can see a reddish to brownish haze along the border of the shadow. This is called the belt of Venus.

Tyndall Scattering Law: The total intensity of radiation scattered by a particle whose size is small compared with the wavelength of the radiation varies inversely as the fourth power of the wavelength. The Tyndall and Rayleigh laws are identical in this regard.

Typhoon: A hurricane that forms over the western Pacific Ocean.

Typhoon: The name for a severe tropical storm in the China Sea or western Pacific. In 1944 off the coast of Luzon in the Philippines sunk 3 American destroyers and downed 146 US aircraft, and took the lives of 790 sailors.