R-loopsSingle-stranded DNA regions in RNA -DNA hybrids formed in vitro under conditions where RNA -DNA duplexes are more stable than DNA -DNA duplexes.
R-ValueA measure of the capacity of a material to resist heat transfer. The R-Value is the reciprocal of the conductivity of a material (U-Value).
R1The first-generation offspring of a recombinant (genetically modified) organism. Not standard terminology. See: T0, T1, and T2.
rachisMain axis of a spike; axis of fern leaf (frond) from which pinnae arise; in compound leaves, the extension of the petiole corresponding to the midrib of…
RADRadiation Absorbed Dose. The basic unit of an absorbed dose of ionizing radiation.
RADAP IIRAdar DAta Processor II, attached to some WSR-57 and WSR-74 radar units. It automatically controls the tilt sequence and computes several radar-derived…
radarAcronym for RAdio Detection And Ranging; a radio device or system for locating an object by means of ultrahigh-frequency radio waves reflected from the…
Radar BeamThe straight line that a radar pulse travels along. As the radar beam gets further away from the radar, it gets wider and wider.
Radar Coded MessageThis is an alphanumeric coded message which will be used in preparation of a national radar summary chart.
Radar Cross SectionThe area of a fictitious, perfect reflector of electromagnetic waves (e.g., metal sphere) that would reflect the same amount of energy back to the radar…
Radar Data AcquisitionAn acronym for Radar Data Acquisition. The RDA is the hardware component of the NEXRAD system that consists of the radar antenna, transmitter, receiver…
radar dopplerThe power spectrum and moments of the radar signal expressed as a function of Doppler frequency or Doppler velocity.
Radar MeteorologyBranch of meteorology that uses radars for weather observations and forecasts.
Radar MosaicA radar product that combines information from multiple radars to give a regional or national view of reflectivity or precipitation.
Radar Product Generator (RPG)The RPG is the computer in the NEXRAD system that receives polar-coordinate base radar data from the RDA and processes these data into end-user products.
Radar RangeDistance from the radar antenna. The WSR-88D radar has a range for velocity products out to 124 nautical miles and reflectivity products out to 248…
Radar ReflectivityThe sum of all backscattering cross-sections (e.g., precipitation particles) in a pulse resolution volume divided by that volume.
Radar Reflectivity Factor (z)z = the sum (over i) of (N_i * D_i^6), where N_i is the number of drops of diameter D_i in a pulse resolution volume.
Radial gateA pivoted crest gate, the face of which is usually a circular arc, with the center of curvature at the pivot about which the gate swings.
Radial Gate (Tainter Gate)A gate with a curved upstream plate and radial arms hinged to piers or other supporting structures on which the gate pivots.
Radial VelocityComponent of motion toward or away from a given location. As "seen" by Doppler radar, it is the component of motion parallel to the radar beam.
radianceA measure of the intensity of the radiant energy flux emitted by a body in a given direction.
Radiant BarrierA thin, reflective foil sheet that exhibits low radiant energy transmission and under certain conditions can block radiant heat transfer; installed in…
Radiant Ceiling PanelsCeiling panels that contain electric resistance heating elements embedded within them to provide radiant heat to a room.
Radiant EnergyEnergy that transmits away from its source in all directions.
Radiant FloorA type of radiant heating system where the building floor contains channels or tubes through which hot fluids such as air or water are circulated.
Radiant Heating SystemA heating system where heat is supplied (radiated) into a room by means of heated surfaces, such as electric resistance elements, hot water (hydronic)…
Radiation(RAY-dee-AY-shun) Energy released in the form of particle or electromagnetic waves.
Radiation BeltMagnetized planets, like Earth, are encircled by zones of particle radiation known as the "Van Allen belts," in which high-energy charged particles spiral…
Radiation FogA fog that forms when outgoing longwave radiation cools the near-surface air below its dew point temperature.
Radiation GasA mixture of photons and fast-moving charged particles.
Radiation hybridA hybrid cell containing small fragments of irradiated human chromosomes. Maps of irradiation sites on chromosomes for the human, rat, mouse, and other…
radiation hybrid cell panel(Abbreviation: RH). A somatic cell hybrid panel in which the chromosomes from the species of interest have been fragmented by irradiation prior to cell…
Radiation LawsThe four physical laws which fundamentally describe the behavior of blackbody radiation: Kirchhoff's law, Planck's law, Stefan-Boltzmann law and Wien's…
Radiation Oncologist(RAY-dee-AY-shun on-KAH-loh-jist) A doctor who specializes in using radiation to treat cancer.
Radiational CoolingThe cooling of the Earth's surface. At night, the Earth suffers a net heat loss to space due to terrestrial cooling.
Radiational InversionUsed interchangably with Nocturnal Inversion; a temperature inversion that develops during the night as a result of radiational cooling of the surface.
Radiative CoolingThe process of cooling by which a heat absorbing media absorbs heat from one source and radiates the heat away.
Radiative ForcingRadiative forcing is the change in the net vertical irradiance (expressed in Watts per square metre: Wm-2) at the tropopause due to an internal change or…
radiative heating rateThe heating rate due to the divergence of long and shortwave radiative flux; this is a calculated quantity using the state of the atmospheric and…
Radiative ZoneA layer of the Sun lying between the core and convection zone where energy travels outward through the slow radiation, absorption, and re-radiation of…
RadiatorA room heat delivery (or exchanger) component of a hydronic (hot water or steam) heating system; hot water or steam is delivered to it by natural…
Radiator VentA device that releases pressure within a radiator when the pressure inside exceeds the operating limits of the vent.
radicleThe portion of the plant embryo which develops into the primary root.
Radio EmissionEmissions of the sun in radio wavelengths from centimeters to dekameters, under both quiet and disturbed conditions. Type I.
Radio EventFlares with Centimetric Bursts and/or definite Ionospheric Event (SID)
Radio WavesElectromagnetic radiation with a wavelength greater than 1 mm (beyond infrared).
Radioactive datingA technique for estimating the age of an object by measuring the amounts of various radioisotopes in it.
Radioactive WasteMaterials left over from making nuclear energy. Radioactive waste can living organisms if it is not stored safely.
RadioactivityThe spontaneous decay of disintegration of an unstable atomic nucleus accompanied by the emission of radiation.
radiocarbon (<sup>14</sup>C)a radioactive isotope of carbon. Since it decays with a half-life of 5570 years, its concentration in organic materials relative to the stable…
radiocarbon datingthe process of providing an absolute age for a material by using measurements of the amount of radiocarbon it still contains.
RadiofacsimileAlso known as HF FAX, radiofax or weatherfax, is a means of broadcasting graphic weather maps and other graphic images via HF radio.
Radioimmunoassay(Abbreviation: RIA). An assay based on the use of a radioactively labelled antibody, where the amount of radiation detected indicates the amount of target…
radioisotope(RAY-dee-oh-I-suh-tope) An unstable form of a chemical element that releases radiation as it breaks down and becomes more stable.
Radioisotope Snow GageA snow water equivalent gage based on the absorption of gamma radiation by snow; this gage can measure up to 55 inches water equivalent with a 2 to 5…
Radionuclide(RAY-dee-oh-NOO-klide) An unstable form of a chemical element that releases radiation as it breaks down and becomes more stable.
RadiosondeAn instrument that is carried aloft by a balloon to send back information on atmospheric temperature, pressure and humidity by means of a small…
RADIUSHorizontal distance from the center of rotation.
Radius of Maximum WindsThe distance from the center of a tropical cyclone to the location of the cyclone's maximum winds.
RadonA toxic gas found in the soil beneath a house that can contribute to cancer and other illnesses.
RainPrecipitation that falls to earth in drops more than 0.5 mm in diameter.
Rain FootSlang for a horizontal bulging near the surface in a precipitation shaft, forming a foot-shaped prominence. It is a visual indication of a wet microburst.
Rain ForestA forest which grows in a region of heavy annual precipitation. There are two major types, tropical and temperate.
rain gageA device, usually a cylindrical container, for measuring rainfall.
Rain GaugeAn instrument for measuring the quantity of rain that has fallen.
Rain Induced FogWhen warm rain falls through cooler air, water evaporates from the warm rain. It subsequently condenses in the cool air forming fog.
Rain ShadowAn area of reduced precipitation on the lee side of a mountain barrier caused by warming of air and dissipation of cloudiness as air descends the barrier.
Rain shadow effectThe region on the lee (sheltered) side of a mountain or mountain range where the precipitation is noticeably less than on the windward side, because the…
Rain ShieldIn a hurricane, a solid or nearly solid area of rain that typically becomes heavier as one approaches the eye.
Rain-free BaseA dark, horizontal cloud base with no visible precipitation beneath it. It typically marks the location of the thunderstorm updraft.
RainbowA flop that contains three different suits, thus no flush can be made on the turn.
RainfallThe amount of precipitation of any type, primarily liquid. It is usually the amount that is measured by a rain gauge.
Rainfall EstimatesA series of NEXRAD products that employ a Z-R relationship to produce accumulations of surface rainfall from observed reflectivity.
rametAn individual member of a clone, descended from the ortet.
Rammed EarthA construction material made by compressing earth in a form; used traditionally in many areas of the world and widely throughout North Africa and the…
Ramp flumeA flume calibrated to measure the flow of liquid in an open channel.
Ramp rateThe rate at power system load or generator output varies, or the limits to such rates due to mechanical or reliability considerations.
random amplified polymorphic DNA(Abbreviation: RAPD). A PCR -based genotyping technique in which genomic template is amplified with single, short (usually 10-mer) randomly chosen primers.
Random earthquakeIn addition to earthquakes that occur on mapped faults, hazards are also presented by earthquakes not associated with known geological structures.