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Glossary of Meteorological Terms

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Glossary of Meteorological Terms Reference Glossary of Meteorological Terms A Aerial: Of or pertaining to the air, atmosphere, or aviation. Also, same as antenna. Absolute humidity: In a system of moist air, the ratio of the Aerograph: In general, any self-recording instrument carried mass of water vapor to the total volume of the system. Usually aloft by any means to obtain meteorological data. expressed as grams per cubic meter (g/m3). Aerometeorograph: A self-recording instrument used on Absolute instrument: An instrument whose calibration can be aircraft for the simultaneous recording of atmospheric determined by means of simple physical measurements on the pressure, temperature, and humidity. instrument. Compare to secondary instrument. AFOS: Automation of Field Operations and Services. A Absolute temperature: Temperature based on an absolute scale. communication system developed in the 1970s by the National Absolute temperature scale: A temperature scale based on Weather Service which utilized minicomputers, video displays, absolute zero. See Kelvin temperature scale. and high-speed communications to replace teletype and facsimile Absolute zero: A hypothetical temperature characterized by a machines. It was replaced by AWIPS in the 1990s. complete absence of heat and defined as 0°K, -273.15°C, or Air current: Very generally, any moving stream of air. It has -459.67°F. no particular technical connotation. Absorption: The process in which incident radiation is retained Air density: The mass density of a parcel of air expressed in by a substance. A further process always results from absorption. units of mass per volume. Absorption hygrometer: A type of hygrometer which Airlight formula: See Koschmieder’s law. measures the water vapor content of the atmosphere by means Air meter: A small anemometer with flat vanes which of the absorption of vapor by a hygroscopic chemical. indicates the number of linear feet or meters of air which have Accretion: Growth of a cloud or precipitation particle by the passed the instrument during its exposure. collision and union of a frozen particle with a super-cooled Albedo: The ratio of the amount of electromagnetic radiation water drop. reflected by a body to the amount incipient upon it, commonly Accuracy: The degree of conformity of an indicated value to expressed as a percentage. The albedo is to be distinguished an accepted standard value, or ideal value. See accuracy from the reflectivity, which refers to one specific wavelength. rating, measured accuracy. Albedometer: An instrument used for the measurement of the Accuracy rating: A number of quantity defining a limit that reflecting power (the albedo) of a surface. A pyranometer errors will not exceed when a device is used under specified adapted for the measurement of radiation reflected from the operating conditions. Accuracy rating can be expressed in a earth’s surface is sometimes employed as an albedometer. number of forms, i.e. in terms of the measured variable ALERT: Automated Local Evaluation in Real Time. Flood (±1°C), percent of span (±0.5% of span), percent of upper warning program, developed by the National Weather Service range value (±0.5% of upper range value F.S.), percent of in the 1970s, that uses remote sensors in the field to transmit scale length (±0.5% of scale length), or percent of actual environmental data to a central computer in real time. output reading (±1% of actual output reading). Allard’s law: A basic equation in night visual range theory, Acid rain: Precipitation that carries to earth sulfuric and nitric relating the illuminance of a point source of light to distance acid accumulated from air pollutants. and the transmissivity of the atmosphere. Acre-foot: The volume of water required to cover one acre to ALOHA: Areal Locations of Hazardous Atmospheres. A a depth of one foot; 43,560 cubic feet. computer model used to predict how a hazardous gas cloud Actinograph: A recording actinometer. might disperse in the atmosphere after an accidental chemical Actinometer: An instrument which measures the intensity of release. Part of the CAMEO system. radiation by determining the amount of chemical change or Alter shield: A type of rain gauge shield consisting of freely fluorescence produced by that radiation. hanging, evenly spaced slats arranged circularly around the Actual pressure: The atmospheric pressure at the level of the gauge. The advantage of this shield is that the slats do not barometer. May or may not be the same as station pressure. easily accumulate snow, permitting its use on unattended Adfreezing: The process by which one object becomes gauges. See rain gauge shield. adhered to another by the binding action of ice. Altimeter: An instrument which determines the altitude of an Adiabatic process: A thermodynamic change of state in a object with respect to a fixed level. There are two general system in which there is no transfer of heat or mass across the types of altimeters: (a) the pressure altimeter, which gives an boundaries of the system. In an adiabatic process, compression approximate measure of altitude from a pressure measurement always results in warming, expansion in cooling. Compare to and an assumed standard temperature distribution; and (b) the diabatic process. radio altimeter, which deduces altitude by electronic Aeolian: Pertaining to the action or effect of the wind. techniques. Derived from the name of the Greek god of the winds, Aeolus. Altimeter setting: The value of atmospheric pressure to which Aeolian anemometer: An anemometer utilizing the principle the scale of a pressure altimeter is set so as to indicate airport that the pitch of the aeolian tones generated by air moving past elevation. The altimeter setting is included as part of an an obstacle is a function of the speed of the air. Largely a aviation weather observation. curiosity and has been put to no practical application in Anabatic wind: An upslope wind due to local surface heating. modern meteorology. Opposite of katabatic wind. NovaLynx Corporation PO Box 240 Grass Valley CA 95945 179 Phone: (530) 823-7185 Fax: (530) 823-8997 USA Toll Free: 1-800-321-3577 www.novalynx.com Reference www.novalynx.com Glossary of Meteorological Terms Analog: Pertaining to measurements or devices in which the Apparent temperature: The perceived temperature derived output varies continuously, i.e. voltage or rotation signals. from either a combination of temperature and wind (wind Compare to digital. chill) or temperature and humidity (heat index). Anemo-biagraph: A recording pressure-tube anemometer in Approximate absolute temperature scale: A temperature which the wind scale of the float manometer has been made scale with the ice point at 273° and boiling point of water at linear by the use of springs, i.e. Dines anemometer. 373°. It is intended to approximate the Kelvin temperature scale Anemoclinograph: A recording anemoclinometer. with sufficient accuracy for many sciences, notably meteorology. Anemoclinometer: General name for a type of instrument ARDC model atmosphere: See standard atmosphere. which measures the inclination of the wind to the horizontal ASCII: American Standard Code for Information Interchange. plane. See bivane. A standard code used to represent data using 8 bits (7 data bits Anemograph: A recording anemometer. and 1 parity bit) per character. Anemometer: A general term for instruments designed to ASOS: Automated Surface Observing System. A network of measure the speed or force of the wind. Italian architect Leon instrumented weather stations deployed primarily by the Battista Alberti invented the first mechanical anemometer in National Weather Service to make weather observations 1450. Derived from the Greek word “anemos,” meaning wind. without operator involvement. Aneroid: Literally “not wet”, containing no liquid. Aspiration meteorograph: An instrument, for the recording Aneroid barograph: An aneroid barometer arranged so that the of two or more meteorological parameters, in which the deflection of the aneroid capsule actuates a pen which graphs a ventilation is provided by a suction fan. record on a rotating drum. Sometimes called aneroidograph. Aspiration psychrometer: A psychrometer in which the Aneroid barometer: A barometer which measures ventilation is provided by a suction fan. atmospheric pressure using one or a series of aneroid capsules. Aspiration thermograph: A thermograph in which ventilation Also called holosteric barometer. is provided by a suction fan. Aneroid capsule: A thin metal disc partially evacuated of air Aspirator: A device attached to a meteorological instrument used to measure atmospheric pressure by measuring its to provide ventilation; usually a suction fan. expansion and contraction. Assmann psychrometer: A special form of the aspiration Aneroidogram: The record of an aneroid barograph. psychrometer, developed by German meteorologist Dr. Richard Angstrom compensation pyrheliometer: An absolute Assmann, in which the thermometric elements are well shielded instrument developed by Swedish physicist Knut Johan from radiation. Psychrometric measurements may be taken with Angstrom (1857-1910) for the measurement of direct solar the instrument in the presence of direct solar radiation. radiation. The radiation receiver station consists of two Asynchronous: Lacking a relationship to a time base or clock. identical manganin strips whose temperatures are measured by In asynchronous communications, individual data characters attached thermocouples. One of the strips is shaded, while the are sent at an arbitrary
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