North Slope of Alaska (NSA) site(NSA)The third ARM research site, the NSA locale has is located in Barrow, Alaska. Its polar regions are predicted to undergo the largest warming in response…
Nuclear electric powerElectricity generated by an electric power plant whose turbines are driven by steam generated in a reactor by heat from the fissioning of nuclear fuel.
Nuclear EnergyEnergy that comes from splitting atoms of radioactive materials, such as uranium, and which produces radioactive wastes.
obliquitythe tilt of the earth's axis of rotation, currently 23.4 degrees.
Observation(OB-ser-VAY-shun) Closely monitoring a patient's condition but withholding treatment until symptoms appear or change.
Observational networkObservational network A group of stations (surface meteorological, upper-air, or other stations) spread over a given area for making regular observations.
Occluded FrontA composite of two fronts, formed as a cold front overtakes a warm or quasi-stationary front.
OilDefined as oil of any kind or in any form including, but not limited to, petroleum, fuel oil, sludge, oil refuse, and oil mixed with wastes.
Oil shaleUnderground formation of a fine-grained sedimentary rock containing varying amounts of kerogen, a solid, waxy mixture of hydrocarbon compounds.
optical depthA measure of how much light airborne particles, whether aersols, cloud droplets, or ice particles, prevent from passing through a column of atmosphere.
orbital cyclesvariations in the Earth's orbit around the sun with periods of 23,000 (precession of the equinoxes), 41,000 (obliquity), and 100,000 years (eccentricity).
OreRock or earth containing workable quantities of a mineral or minerals of commercial value.
Organic compoundAn organic compound contains carbon chemically bound to hydrogen. Organic compounds often contain other elements (particularly O, N, halogens, or S).
Organic fertilizerOrganic material such as manure or compost, applied to cropland as a source of plant nutrients.
ostracoda small crustacean that lives in either the ocean or in freshwater.
OxidizeTo chemically transform a substance by combining it with oxygen.
Oxygen cycleCyclic movement of oxygen in different chemical forms from the environment, to organisms, and then back to the environment.
oxygen isotope ratio (δ<sup>18</sup>O)an expression for the ratio of the two isotopes 18O to 16O in a sample relative to a standard, defined as: δ18O= (18O/16Osample - 18O/16Ostandard)/…
OzoneTropospheric ozone (ground-level ozone), or smog, is formed when volatile organic compounds, oxygen and nitrogen oxides react in the presence of sunlight.
Ozone (O3)A strong-smelling, reactive, toxic, chemical gas consisting of three oxygen atoms chemically attached to each other.
Ozone (O<sub>3</sub>)A colorless gas with a pungent odor, having the molecular form of O3 , found in two layers of the atmosphere, the stratosphere (about 90% of the total…
Ozone Depleting Substance (ODS)A family of man-made compounds that includes, but are not limited to, chlorofluorocarbons (CFCs), bromofluorocarbons (halons), methyl chloroform, carbon…
Ozone LayerAn atmospheric layer that contains a high proportion of oxygen that exists as ozone.
Ozone PrecursorsChemical compounds, such as carbon monoxide, methane, non-methane hydrocarbons, and nitrogen oxides, which in the presence of solar radiation react with…
Ozone shieldOzone shield Stratospheric ozone layer, giving protection to the Earth's surface due to intense absorption of harmful solar ultraviolet radiation by the…
paleoenvironmental proxyan environmental relict (pollen grains, tree rings, lake sediments, pack rat middens, ice cores, coral skeletons) that is used by scientists to infer past…
parameterA value or measurement that varies with circumstances, and is used as a reference to quantify a situation or a process.
particle size distributionThe number of particles present in any given volume of air within a specified size range.
ParticulateA small, discrete mass of solid or liquid matter that remains individually dispersed in gas or liquid emissions.
Particulate Matter (PM)Very small pieces of solid or liquid matter such as particles of soot, dust, fumes, mists or aerosols.
ParticulatesThe fine liquid or solid particles contained in combustion gases. The quantity and size of particulates emitted by cars, power and industrial plants, wood…
Parts per billion (ppb)A measurement of concentration on a weight or volume basis. Equivalent to micrograms per liter.
Parts per million (ppm)A measurement of concentration on a weight or volume basis. Equivalent to milligrams per liter (mg/l).
Past weatherPast weather Predominant characteristic of the weather which had existed at an observing station during a given period of time (during the preceding hour…
Pentanes plusA mixture of hydrocarbons, mostly pentanes and heavier fractions, extracted from natural gas. See hydrocarbons.
Perfluorocarbons (PFCs)A group of human-made chemicals composed of carbon and fluorine only. These chemicals (predominantly CF4 and C2F6) were introduced as alternatives, along…
Petrochemical feedstockFeedstock derived from petroleum, used principally for the manufacture of chemicals, synthetic rubber, and a variety of plastics.
PetrochemicalsChemicals obtained by refining (i.e., distilling) crude oil. They are used as raw materials in the manufacture of most industrial chemicals, fertilizers…
PetroleumAny petroleum-based substance composed of a complex blend of hydrocarbons derived from crude oil, including motor fuel, jet oil, lubricants, petroleum…
Petroleum cokeA residue that is the final product of the condensation process in cracking.
PhotosynthesisA chemical process by which green plants synthesize organic compounds from carbon dioxide and water in the presence of sunlight.
Photovoltaic and solar thermal energyEnergy radiated by the sun as electromagnetic waves (electromagnetic radiation) that is converted into electricity by means of solar (i.e.
Pilot Balloon(Abbrev. PIBAL)- A small helium-filled meteorological balloon that is tracked as it rises through the atmosphere to determine how wind speed and direction…
Planetary Boundary LayerThe layer within the atmosphere between 1 km and the earth's surface where friction affects wind speed and wind direction.
PlanktonCollectively, all organisms (plants and animals) suspended in the water which are not independent of water movements.
planktonic foraminiferaMarine zooplankton that passively float or weakly swim, and have calcium carbonate skeletons that are present in large numbers on the surface of the ocean.
Pleistocene epochAn interval of the Quaternary period, from 1.8 million to about 11,500 years before present.
Point sourceAny discernible, confined, or discrete conveyance from which pollutants are or may be discharged, including, but not limited to, any pipe, ditch, channel…
Polar dayPolar day In polar regions, the portion of the year when the Sun is continuously in the sky.
Polar explorerPolar explorer A person working for a long time at one of the polar observing stations. Russian word is "polyarnik."
Polar lowPolar low Small, shallow depression which forms mainly in winter over some high-latitude seas within a polar or arctic air mass.
Polar nightPolar night In polar regions, the portion of the year when the Sun does not rise above the horizon.
Polar vortexPolar vortex Large-scale cyclonic circulation in the middle and upper troposphere centered generally in the polar regions.
PollutionA resource that is out of place. Generally, the presence of matter or energy whose nature, location or quantity produces undesired environmental effects.
Polyvinyl Chloride (PVC)A type of plastic used to make pipe and fittings for water distribution and irrigation.
Populationthe totality of items or units of material under consideration.
positive feedbackthe process in which an initial change will bring about an additional change in the same direction.
Potential TemperatureThe temperature a parcel of dry air would have if brought adiabatically (i.e., without transfer of heat or mass) to a standard pressure level of 1000 mb.
PrecessionThe comparatively slow torquing of the orbital planes of all satellites with respect to the Earth's axis, due to the bulge of the Earth at the equator…
precession (of the equinoxes)the slow clockwise motion of the equinoxes along the path of the earth's orbit due to the wobble of the earth's axis.
Precipitable WaterMeasure of the depth of liquid water at the surface that would result after precipitating all of the water vapor in a vertical column over a given…
PrecipitationThe total measurable amount of water received in the form of snow, rain, drizzle, hail, and sleet.
PrecisionThe accuracy with which a number can be represented, i.e., the number of digits used to represent a number.
preliminary dataData that have not necessarily been subjected to review, quality control and/or documentation by a responsible investigator.
Prescribed burningDeliberate setting and careful control of surface fires in forests to help prevent more destructive fires and to kill off unwanted plants that compete…
Present WeatherThe type of weather observed at the reporting time. These conditions may include types and intensity of precipitation such as light rain or heavy snow, as…
PressureThe load divided by the area over which it acts.
Pressure TendencyThe character and amount of atmospheric pressure change during a specified period of time, usually 3-hour period preceding an observation.
prevailing windThe wind direction most frequently observed during a given period.
Primary oil recoveryPumping out the crude oil that flows by gravity into the bottom of an oil well. See enhanced oil recovery, secondary oil recovery.
Problem Identification Form (PIF)(PIF)Used to identify and document problems with ARM systems, physical infrastructure, or instruments.
ProxyIf you own common stock in a US corporation, you have the right to vote on certain company policies and elect the board of directors by casting a proxy…
PsychrometerAn instrument for measuring relative humidity by means of wet and dry-bulb temperatures.
Psychrometric tablesPsychrometric tables Tables prepared from the psychrometric formula and used to obtain vapor pressure, relative humidity, and dew point from wet- and…
PyranometerA device used to measure total incident solar radiation (direct beam, diffuse, and reflected radiation) per unit time per unit area.
Quality Measurement Experiments (QME)(QME)A special class of value-added product that regularly compares two or more data sets intended to understand the individual datastreams either as functions…
quality-assured dataTypically, the final form of data to be submitted to the ARM data system. Includes datastream description documentation, fully calibrated data in commonly…
Quaternary periodthe second period of the Cenozoic era containing the Pleistocene epoch and the Holocene epoch and lasting from 1.8 million years to the present.
Quick LooksDaily and weekly plots of ARM data that give users a browsable quick view of a subset of data available at the ARM Archive.
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 dopplerThe power spectrum and moments of the radar signal expressed as a function of Doppler frequency or Doppler velocity.
Radar ReflectivityThe sum of all backscattering cross-sections (e.g., precipitation particles) in a pulse resolution volume divided by that volume.
radianceA measure of the intensity of the radiant energy flux emitted by a body in a given direction.
Radiation(RAY-dee-AY-shun) Energy released in the form of particle or electromagnetic waves.
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…
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.
RadiosondeAn instrument that is carried aloft by a balloon to send back information on atmospheric temperature, pressure and humidity by means of a small…