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Traveltime tomography
Traveltime tomography is an inverse method that reconstructs a medium's internal velocity structure from measured wave travel times, imaging the Earth's subsurface from oil fields to the entire mantle.
Tremolite
Tremolite is a calcium amphibole mineral with the ideal formula Ca2Mg5Si8O22(OH)2, the magnesium-rich end of a series with actinolite; its asbestiform variety is a regulated asbestos mineral.
Trewartha climate classification
The Trewartha climate classification, often called the Köppen–Trewartha classification, is a 1966 modification of the Köppen system by geographer Glenn Trewartha, subdividing middle latitudes into temperature-based groups.
Triassic
The Triassic, the first period of the Mesozoic Era, ran from about 252 to 201 million years ago, saw the first dinosaurs, and opened after Earth's largest mass extinction.
Triassic–Jurassic extinction
The Triassic–Jurassic extinction, also called the end-Triassic extinction, was a mass extinction about 201 million years ago, likely caused by massive CAMP volcanic eruptions as Pangea broke apart.
Tridymite
Tridymite is a polymorph of silica, chemically identical to quartz but with a different crystal structure, found chiefly in siliceous volcanic rocks, some opals, and certain meteorites.
Trieste (bathyscaphe)
Trieste was a deep-diving research bathyscaphe designed by Auguste Piccard, built in Italy, and launched in 1953; in 1960 Jacques Piccard and Don Walsh piloted it to the Challenger Deep.
Triple divide
A triple divide, also called a triple watershed or hydrological apex, is where two continental divides intersect, letting water drain into three different watersheds, as at Montana's Triple Divide Peak.
Triple junction
A triple junction is the point where the boundaries of three tectonic plates meet, the only stable configuration on a sphere; the Afar and Mendocino junctions are classic examples.
Triple oxygen isotope analysis
Triple oxygen isotope analysis measures the relative abundances of the stable oxygen isotopes ¹⁶O, ¹⁷O, and ¹⁸O, quantifying deviations that record temperatures, hydrologic processes, and atmospheric chemistry.
Trondhjemite
Trondhjemite is a leucocratic intrusive igneous rock, defined as a tonalite with mafic minerals below 10 percent, named by Victor Moritz Goldschmidt in 1916 after Trondheim, Norway.
Trophic cascade
A trophic cascade is an indirect interaction in which a top predator's effects propagate down a food web to herbivores and plants, introduced by ecologist Robert Paine.
Trophic state index
The trophic state index, also known as Carlson's Trophic State Index, is a 0 to 100 scale classifying lake productivity, developed by Robert E. Carlson in 1977.
Tropical climate
A tropical climate is a continually hot climate of equatorial and tropical regions with considerable precipitation, forming Köppen group A with all months above 18 °C.
Tropical cyclogenesis
Tropical cyclogenesis is the process by which a tropical cyclone forms, typically progressing from a tropical disturbance through depression and storm stages to a full cyclone.
Tropical cyclone
A tropical cyclone is a warm-core, rotating low-pressure storm that forms over warm tropical or subtropical waters, called a hurricane, typhoon, or cyclone depending on the region.
Tropical cyclone heat potential
Tropical cyclone heat potential (TCHP) is an ocean measure of the heat available to a tropical cyclone, integrated from the surface to the 26 °C isotherm.
Tropical cyclone naming
Tropical cyclone naming is the practice of assigning short, distinctive names to tropical storms so warnings are unambiguous, with names retired after deadly or costly storms.
Tropical cyclone observation
Tropical cyclone observation is the measurement of a cyclone's position, intensity, size, and structure using aircraft reconnaissance, satellites, radar, buoys, and ships, so forecasters can analyze storms and verify forecast models.
Tropical cyclone preparedness
Tropical cyclone preparedness, or hurricane preparedness, covers the household planning, warning systems, evacuation, and structural mitigation used to reduce deaths, injuries, and property damage from tropical cyclones.
Tropical cyclone warnings and watches
Tropical cyclone warnings and watches are official alerts issued when a tropical cyclone threatens a coast, with a watch meaning possible conditions and a warning expected ones.
Tropical cyclone watch and warning
A tropical cyclone watch or warning is an official announcement that hazardous wind or storm surge conditions are possible (watch) or expected (warning) in a coastal area.
Tropical cyclones in 2022
Tropical cyclones in 2022 produced 85 named storms worldwide, near average, under a rare third consecutive La Niña, with record-low strength and Hurricane Ian costing $113 billion.
Tropical cyclones in 2024
Tropical cyclones in 2024 produced a near-average 85 named storms worldwide but about 21% below-average energy, with an above-normal Atlantic season and Typhoon Yagi killing roughly 850 people.
Tropical cyclones in 2026
Tropical cyclones in 2026 formed worldwide under a strong El Niño, which drove record eastern Pacific activity while the Atlantic stayed quiet until Hurricane Isaias formed in October.
Tropical depression
A tropical depression is the weakest classified stage of a tropical cyclone, with sustained winds of 33 knots (38 mph) or less and a closed circulation.
Tropical disturbance
A tropical disturbance is an organized cluster of tropical thunderstorms, generally 200 to 600 km wide, and the first stage in the development of a tropical cyclone.
Tropical easterly jet
The tropical easterly jet is a band of strong east-to-west winds in the upper troposphere near 15°N, a semi-permanent feature of the summer monsoon whose position shapes monsoon rainfall.
Tropical instability waves
Tropical instability waves (TIWs) are westward-propagating ocean waves with wavelengths near 1,000 km and periods of weeks, arising from shear between the Pacific and Atlantic equatorial currents.
Tropical monsoon climate
A tropical monsoon climate, abbreviated Am in the Köppen system, is a tropical climate with seasonally reversing winds, a pronounced rainy season, and a short dry season.