751 articles
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 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.
Tsunami
A tsunami, also called a seismic sea wave, is a series of ocean waves usually generated by a large undersea earthquake that suddenly displaces the water column.
Turbidity current
A turbidity current is a rapid downslope flow of sediment-laden water, the main way sediment reaches the deep ocean, breaking seabed cables as it goes.
Ultra-short baseline positioning
Ultra-short baseline (USBL) positioning is an underwater acoustic technique that determines the 3D position of submerged targets, such as ROVs, from a single compact transducer array on a surface vessel.
Unconfined aquifer
An unconfined aquifer, or water-table aquifer, is a groundwater layer whose upper boundary is the water table, which recharges directly from the surface and is vulnerable to drought and contamination.
Undertow (water waves)
Undertow, also called bed return flow, is the wave-driven seaward return flow near the seabed in the surf zone, compensating for the onshore transport by breaking waves.
Unimpaired runoff
Unimpaired runoff, also called full natural flow, is the flow a river would carry without dams or diversions, estimated by removing human effects from measured flows.
Unit hydrograph
A unit hydrograph is the direct runoff hydrograph resulting from one unit depth of rainfall excess falling uniformly over a watershed, introduced by LeRoy Sherman in 1932.
United Kingdom Hydrographic Office
The United Kingdom Hydrographic Office is a Ministry of Defence agency founded in 1795 that publishes ADMIRALTY charts used by over 90% of large international ships.
United States Hydrographic Office
The United States Hydrographic Office, also known as the U.S. Naval Hydrographic Office, was the U.S. Navy's charting agency from 1866 until 1962, chiefly for foreign waters.
University-National Oceanographic Laboratory System
The University-National Oceanographic Laboratory System, or UNOLS, is a consortium of 61 academic institutions that coordinates access to the U.S. Academic Research Fleet, founded in 1971.
Unmanned underwater vehicle
An unmanned underwater vehicle (UUV), also called an underwater drone or robotic submarine, is a robot operating underwater without a human aboard, either tethered and remotely piloted or autonomous.
Upsweep
Upsweep is a long-running, unidentified underwater sound in the South Pacific, recorded by NOAA's hydrophones since August 1991 and loud enough to be heard across the Pacific.
Ur Schatt
The Ur Schatt, also written Ur-Schatt or Ur-Shatt, was the combined Tigris-Euphrates-Karun river that flowed along the exposed Persian Gulf floor into the Gulf of Oman about 15,000 years ago.
V-notch weir
A V-notch weir is a sharp-crested, thin-plate weir with a triangular notch used to measure small water flows in open channels, its triangular shape giving it sensitivity at low discharges.
Vadose zone
The vadose zone, also called the unsaturated zone, is the subsurface layer between the land surface and the water table, where pores hold both air and water.
Van Veen grab
The Van Veen grab is a bottom sampler with two scoop-like jaws closed by the pull of the deployment line, developed by Dutch engineer Johan van Veen.
Variable source area
A variable source area is the part of a catchment that generates storm runoff, expanding and shrinking as soils become saturated, a concept developed by John D. Hewlett in the 1960s.
Varve chronology
Varve chronology counts annual sediment layers, called varves, to date and correlate sedimentary sequences with calendar-year precision; the Swedish geologist Gerard De Geer proposed it in 1884.
Victor Hensen
Victor Hensen (Christian Andreas Victor Hensen, 1835–1924) was a German physiologist at the University of Kiel who coined the term "plankton" and founded quantitative plankton research.
VIIRS
VIIRS (Visible Infrared Imaging Radiometer Suite) is a scanning radiometer on US polar-orbiting satellites, first launched in 2011, that images Earth's land, oceans, and atmosphere twice daily.
Viktor Schauberger
Viktor Schauberger (1885–1958) was an Austrian forester, naturalist, and inventor who built log flumes and developed water- and air-driven machines based on what he called implosion.
Vitus Bering
Vitus Jonassen Bering (1681–1741) was a Danish-born navigator in the Russian navy who led the Kamchatka expeditions, proved Asia and America are separated by sea, and reached Alaska in 1741.
Walker Lake (Nevada)
Walker Lake is a terminal lake in Mineral County, Nevada, fed by the Walker River with no outlet. Agricultural diversions have shrunk it and killed its native fish.
Water balance
A water balance, also called a water budget, is an accounting of water entering, leaving, and stored within a system such as a watershed, based on conservation of mass.
Water content
Water content, also known as moisture content, is the amount of water held in a soil, expressed gravimetrically by mass or volumetrically, and widely monitored in agriculture and hydrology.
Water cycle
The water cycle, also called the hydrologic cycle, is the continuous movement of water among oceans, atmosphere, and land, driven by solar energy and gravity.
Water distribution on Earth
Water distribution on Earth describes how about 332.5 million cubic miles of water is split among oceans, ice, groundwater, and surface waters, with over 96 percent saline.