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Regional Ocean Modeling System
The Regional Ocean Modeling System (ROMS) is an open-source, three-dimensional ocean circulation model developed at Rutgers University and UCLA and used in NOAA coastal forecasts.
Regolith
Regolith is the layer of loose, fragmented rock material that overlies bedrock, formed by weathering, erosion, transport, or deposition, covering Earth, the Moon, and Mars.
Regulated river
A regulated river is one whose flow is largely controlled by major man-made structures such as dams and weirs, so water can be released from upstream storage on demand.
Relative dating
Relative dating is a set of geological and archaeological methods for placing rocks, fossils, and artifacts in chronological order without assigning numerical ages in years.
Relative humidity
Relative humidity is the ratio, expressed as a percent, of water vapor in the air to the amount that would saturate it at the same temperature.
Remaining carbon budget
The remaining carbon budget is the net CO2 humans can still emit while keeping warming below a temperature limit with a stated probability, key to Paris Agreement goals.
Remotely operated underwater vehicle
A remotely operated underwater vehicle, or ROV, is a tethered underwater robot piloted in real time from a surface ship, first developed by the U.S. Navy in the 1960s.
Renewable resource
A renewable resource, also called a flow resource, is a natural resource like water, forests, fish, or sunlight that regenerates on a timescale relevant to human use.
Representative Concentration Pathway
A Representative Concentration Pathway (RCP) is one of four greenhouse gas and land use scenarios used in climate modeling, named for its radiative forcing by 2100.
Research vessel
A research vessel, also called a research ship or oceanographic research ship, is a specialized ship carrying laboratories, sensors, and facilities for oceanographic research at sea.
Reservoir sedimentation
Reservoir sedimentation is the accumulation of sediment carried by a river inside the artificial lake behind a dam, which gradually reduces storage capacity; reservoirs worldwide lose 0.5% to 1.0% of storage each year.
Residual amount of water
Residual amount of water (residual flow): the flow left in a river below a dam or water take to sustain ecosystems, also called minimum, instream, or environmental flow; key in hydropower reduced flow stretches like Belo Monte.
Residual circulation
Residual circulation is the net large-scale ocean overturning flow, the sum of Eulerian-mean and eddy-induced circulation, and it transports heat, carbon, and nutrients across the Southern Ocean.
Resistivity meter
A resistivity meter is a geophysical field instrument that injects electric current through electrodes and measures voltage to determine subsurface resistivity, supporting groundwater exploration, mineral prospecting, and archaeology.
Resolution Copper
Resolution Copper is a proposed underground copper mine near Superior, Arizona, a Rio Tinto and BHP joint venture atop one of the world's largest undeveloped copper deposits.
Retrograde metamorphism
Retrograde metamorphism is the stage of a metamorphic rock's history in which pressure and temperature decrease during exhumation toward the surface, partially overprinting minerals formed at peak conditions.
Return period
A return period, or recurrence interval, is the average time in years between hydrologic events of a given size, such as a flood exceeding a set discharge.
Reventador
Reventador (Volcán El Reventador), Ecuadorian andesitic stratovolcano 90 km east of Quito, 3,562 m; VEI 4 eruption 3 November 2002; continuously active since 2008 with daily explosions, ash plumes, and lava flows; Alert Level Orange.
Reverse circulation drilling
Reverse circulation drilling is a percussive exploration method in which compressed air carries rock chips up an inner tube, giving clean samples for mineral exploration and grade control.
Reverse time migration
Reverse time migration (RTM) is a seismic imaging method that propagates recorded wavefields backward in time using the full two-way wave equation, introduced in the early 1980s.
Revised Universal Soil Loss Equation
The Revised Universal Soil Loss Equation (RUSLE) is an empirical model estimating annual soil loss from water erosion, released in 1992 as a computerized USLE.
Rhine Graben
The Rhine Graben is a 300-km-long rift valley along the Rhine between Basel and the Rhenish Massif, forming the central segment of the European Cenozoic Rift System.
Rhumb line
A rhumb line, also called a loxodrome, crosses every meridian at the same angle, letting a ship or aircraft hold a constant bearing; it appears straight on a Mercator chart.
Rhyolite
Rhyolite is a fine-grained, silica-rich extrusive igneous rock, the volcanic equivalent of granite, usually pink, buff, or light gray and typically formed in rare, often violent eruptions.
Richards equation
Richards equation is the nonlinear partial differential equation describing water movement in unsaturated porous media, formulated by Lorenzo A. Richards in his 1931 paper in Physics.
Ridge
A ridge, or mountain ridge, is an elongated elevation with a narrow crest, formed by tectonic folding, erosion, glacial or coastal deposition, or cooling-planet contraction.
Rift valley
Rift valley: an elongated trough formed where lithosphere stretches between normal faults, as in the East African Rift, Baikal Rift, and Rhine Valley; some rifts become ocean basins, others fail and stay dormant.
Rill erosion
Rill erosion is the removal of soil by runoff water concentrated into numerous small, generally parallel channels centimeters deep; untreated, it develops into gully erosion.
Rime ice
Rime ice is a white, milky, opaque deposit of granular ice that forms when supercooled fog or cloud droplets freeze rapidly on striking a cold surface.
Riming
Riming is the cloud physics process by which supercooled liquid droplets freeze onto falling ice particles, one of three major ice crystal growth mechanisms in clouds.