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Cyclone phase space
The cyclone phase space (CPS) is a three-dimensional diagnostic framework introduced by Robert E. Hart in 2003 that classifies cyclones as tropical, extratropical, or hybrid.
Cyclone Remal
Remal was the first severe cyclonic storm of the 2024 Bay of Bengal season, making landfall in May across Bangladesh and West Bengal, killing 22 people.
Cyclone Senyar
Cyclone Senyar was a rare November 2025 tropical cyclone over the Strait of Malacca whose floods and landslides killed over 1,100 people in Sumatra, Malaysia, and Thailand.
Cyclone Seroja
Severe Tropical Cyclone Seroja was a category 3 cyclone of April 2021 that caused deadly floods in Indonesia and Timor-Leste before an unusually far-south landfall near Kalbarri, Western Australia.
Cyclone Sidr
Cyclone Sidr was a tropical cyclone that formed over the Bay of Bengal and struck Bangladesh on 15 November 2007, killing roughly 3,400 to 4,200 people.
Cyclone Tauktae
Cyclone Tauktae was an extremely severe cyclonic storm in the Arabian Sea in May 2021 that tracked India's entire west coast and made landfall in Gujarat on May 17.
Cyclone Titli
Cyclone Titli was a very severe cyclonic storm that struck the north Andhra Pradesh and south Odisha coast of India on 11 October 2018, killing at least 93 people.
Cyclone Tracy
Severe Tropical Cyclone Tracy was a small but intense cyclone that struck Darwin, Australia, on Christmas Day 1974, killing 66 people and prompting Australia's largest peacetime evacuation.
Cyclone Vaianu (2026)
Cyclone Vaianu was a Category 3 South Pacific tropical cyclone that hit New Zealand's North Island on 12 April 2026, forcing hundreds of households to evacuate.
Cyclone Winston
Cyclone Winston was a Category 5 tropical cyclone that struck Fiji in February 2016, killing 44 people as the most intense cyclone on record there.
Cyclone Yaas
Cyclone Yaas was a very severe cyclonic storm over the Bay of Bengal that struck the north Odisha and West Bengal coasts of India on 26 May 2021.
Cyclone Yasi
Severe Tropical Cyclone Yasi was a Category 5 cyclone that crossed the Queensland coast near Mission Beach on 3 February 2011, the strongest landfall there since at least 1918.
Cyclostratigraphy
Cyclostratigraphy is the branch of stratigraphy that identifies and interprets cyclic variations in the stratigraphic record, most often those driven by Milankovitch orbital cycles, to build precise geological time scales.
Cylindrospermopsin
Cylindrospermopsin is an alkaloid toxin produced by freshwater cyanobacteria that inhibits protein synthesis, damaging the liver and kidneys. First isolated in 1992, it was the likely cause of a 1979 mass poisoning on Palm Island, Australia.
D″ layer
The D″ layer is the lowermost 200 to 300 km of Earth's mantle, lying directly above the core-mantle boundary at about 2,900 km depth and seismically distinct from the lower mantle.
Dabie–Sulu orogenic belt
The Dabie–Sulu orogenic belt is a Triassic continental collision zone in east-central China marking the suture between the North China Craton and the Yangtze Block.
Dakota Sandstone
The Dakota Sandstone is a widespread Cretaceous sandstone unit named from Dakota County, Nebraska, mapped across the Great Plains and Colorado Plateau in 14 states.
Damage indicator (tornado)
A damage indicator (DI) is one of 28 standardized structures, trees, or objects used to rate tornado intensity on the Enhanced Fujita (EF) scale, operational since 2007.
Danian
The Danian is the lowest stage of the Paleocene Epoch, spanning 66.0 to 61.66 million years ago and beginning at the mass extinction that ended the dinosaurs.
Dansgaard–Oeschger event
A Dansgaard–Oeschger event (D-O event), named for Willi Dansgaard and Hans Oeschger, is one of about 25 abrupt millennial-scale climate oscillations of the last glacial period.
Daphnia magna
Daphnia magna, commonly called the water flea, is a small freshwater planktonic crustacean living in ponds and lakes across Europe and North America, and a standard test organism in aquatic ecotoxicology.
Daphnia pulex
Daphnia pulex, commonly called the water flea, is a widespread freshwater crustacean that grazes algae in lakes and ponds and was the first crustacean to have its genome sequenced.
Darcy's law
Darcy's law is an empirical law of groundwater flow stating that flow through a porous medium is proportional to the hydraulic gradient, published by Henry Darcy in 1856.
Data assimilation
Data assimilation is a family of numerical methods that combine observations with numerical model forecasts to estimate the evolving state of systems such as the atmosphere or ocean.
Daulatpur–Saturia tornado
The Daulatpur–Saturia tornado struck the Manikganj district of central Bangladesh on April 26, 1989, killing an estimated 1,300 people, the deadliest tornado in world records.
DBZ (meteorology)
DBZ, or decibels relative to Z, is a logarithmic unit used in weather radar to measure radar reflectivity from precipitation, with values above about 50 dBZ indicating hail.
De Geer chronology
The De Geer chronology, formally the Swedish Time Scale, is a year-by-year timeline built from counting glacial varves, assembled by Swedish geologist Gerard De Geer from 1882 onward.
De Martonne aridity index
The De Martonne aridity index (DMI) is a climatic index that classifies a location's dryness as annual precipitation in millimeters divided by mean annual temperature in degrees Celsius plus 10.
Dead Sea (ים המלח)
The Dead Sea (ים המלח) is a hypersaline terminal lake in the Jordan Rift Valley between Jordan and Israel, about ten times saltier than the ocean.
Dead Sea Transform
The Dead Sea Transform, also called the Dead Sea Fault, is a roughly 1,000-km-long left-lateral fault system between the Arabian plate and the Sinai subplate.