Glossary of Meteorological Terms (B)

B

Backing

A change in wind direction in a counterclockwise sense; opposite of veering.

Backlash

The play or loose motion in an instrument due to the clearance existing between mechanically contacting parts.

Backplane

Area of a computer or other device where various logic and control elements are interconnected. Often a printed circuit board into which other circuit boards plug at right angles.

Balloon

See captive balloon, ceiling balloon, constant-level balloon, free balloon, hurricane beacon, kytoon, Moby Dick balloon, pilot balloon, radiosonde balloon, rockoon, skyhook balloon, transosonde.

Balloon ceiling

The ceiling classification which is applied when the ceiling height is determined by timing the ascent and disappearance of a ceiling balloon or pilot balloon.

Balloon cover

A cover which fits over a large inflated balloon to facilitate handling in high or gusty winds.

Balloon drag

A small balloon, loaded with ballast and inflated so that it will explode at a predetermined altitude, which is attached to a larger balloon.

Balloon shroud

Same as balloon cover.

Bandwidth

The number of cycles per second between the limits of a frequency band.

Bankfull stage

The stage, on a fixed river gauge, corresponding to the top of the lowest banks within the reach for which the gauge is used as an index. Compare to flood stage.

Bar

A unit of pressure equal to 106 dyne per cm² (106 barye), 1000 millibars, 29.53 inches of mercury.

Barogram

The record of a barograph.

Barograph

A continuous-recording barometer.

Barometer

An instrument for measuring the pressure of the atmosphere. The two principal types are aneroid and mercurial.

Barometric altimeter

Same as pressure altimeter.

Barometric column

Same as mercury column.

Barometric constant

Factor relating the pressure and the height of a column of mercury, for example, 1 mb = 0.750062 mm, 1 mm = 1.333224 mb.

Barometric correction table

Table or graph to facilitate compensation of the instrumental errors of a mercury barometer. The required compensation is generally very small and is normally included in the barometric reduction table. See compensation of instruments.

Barometric corrections

The corrections that must be applied to the reading of a mercury barometer in order that this observed value may be rendered accurate. There are four kinds. (1) The instrument correction is the mean difference between the readings of a given mercury barometer and those of a standard instrument. It is a composite correction, including the effects of capillarity (see capillarity correction), index misalignment, imperfect vacuum, and scale correction, which are the barometric errors. (2) The temperature correction is applied to account for the difference between the coefficient of expansion of mercury and that of the scale. (3) The gravity correction is necessary because the acceleration of gravity varies with both altitude and latitude. (4) The removal correction is applied when the barometer elevation differs from the adopted station elevation and/or climatological station elevation. See also capacity correction. U.S. Weather Bureau, 1941: Barometers and the Measurement of Atmospheric Pressure, Circular F, 7th ed., rev

Barometric errors

See barometric corrections.

Barometric hypsometry

The technique of estimating elevation by means of atmospheric pressure measurements.

Barometric pressure

Same as atmospheric pressure.

Barometry

The art or process of making barometrical measurements.

Baroswitch

A pressure-operated switching device used in a radiosonde. In operation, the expansion of an aneroid capsule causes an electrical contact to scan a radiosonde commutator composed of conductors separated by insulators.

Barothermograph

An instrument that automatically records pressure and temperature.

Basin

See river basin.

Basin accounting

See hydrologic accounting.

Basin lag

A computed characteristic of a particular river basin, expressed as the time difference between the time-center of mass of rainfall and the time-center of mass of resulting runoff.

Basin recharge

The difference between amounts of precipitation and runoff for a given storm. It is that portion of the precipitation that remains in the basin as soil moisture, surface storage, ground water, etc.

Baud

A unit of signaling speed representing the number of code elements sent per second; often, bits per second.

BCD

Binary Coded Decimal. A coding system in which each decimal digit from 0 to 9 is represented by a 4-digit binary number.

Beaufort wind scale

A system of estimating and reporting wind speed, originally based on the effect of various wind speeds on the amount of canvas that a full-rigged nineteenth century frigate could carry.

Bellani atmometer

An instrument which measures evaporation by measuring the loss of water from a burette reservoir through a ceramic disc.

Bellows

See aneroid capsule.

Bimetallic thermometer

A thermometer, the sensitive element of which consists of two metal strips which have different coefficients of expansion and are brazed together. The distortions of the system in response to temperature variations are used as a measure of temperature. It is a type of deformation thermometer.

Bimetal strip

See bimetallic thermometer.

Binary

A numbering system using a base number of 2 and having only two digits: 0 and 1. The fundamental system of representing information with electrical pulses.

Bit

Abbreviation for binary digit. The smallest unit of information, equal to one binary decision, i.e. 1/0, on/off, yes/no.

Bivane

A wind vane used to obtain the horizontal and vertical components of the wind.

Black body

A hypothetical, ideal body which absorbs completely all incident radiation, independent of wavelength and direction. No actual substance behaves as a true black body, although platinum black and other soots rather closely approximate this ideal. However, one does speak of a black body with respect to a particular wavelength interval. Compare to gray body, white body.

Black-bulb thermometer

A thermometer whose sensitive element has been made to resemble a black body by covering it with lamp black. The thermometer is placed in an evacuated transparent chamber which is maintained at a constant temperature. The instrument responds to insolation, modified by the transmission characteristics of its container.

Blizzard

A severe weather condition characterized by low temperatures and strong winds bearing a great amount of snow, either falling or picked up from the ground.

Boiling point

Temperature of equilibrium between the liquid and vapor phases of a substance at a given pressure.

Bologram

The record obtained from a bolometer.

Bolometer

Instrument for measuring the intensity of radiant energy. Its principle is based on the variation of electrical resistance, with the incoming radiation, of one or both the metallic strips which the instrument comprises.

Bottle thermometer

A thermoelectric thermometer used for measuring air temperature. The name is derived from the fact that the reference thermocouple is placed in an insulated bottle.

Bourdon tube

Closed, curved, flexible tube of elliptic cross section which is deformed, according to type, by variations of atmospheric pressure or temperature and so provides a measurement of the particular parameter.

Breeze

Wind with a speed between 4 and 27 knots (4 and 31 mph); Beaufort scale numbers 2 through 6.

Bridled-cup anemometer

A combination cup anemometer and pressure-plate anemometer, consisting of an array of cups about a vertical axis of rotation, the free rotation of which is restricted by a suitable spring arrangement.

British thermal unit

A unit of energy defined as the heat required to raise the temperature of one pound of water one degree Fahrenheit. It is equal to 252.1 calories or to 1055 joules.

Brontometer

A general term to designate apparatus designed to observe the details of weather during thunderstorms.

Bucket thermometer

A water-temperature thermometer provided with an insulated container around the bulb. It is lowered into the sea on a line until it has had time to reach the temperature of the surface water, then withdrawn and read. The insulated water surrounding the bulb preserves the temperature reading and is available as a salinity sample.

Burst

A radar term for a single pulse of radio energy.

Bus

A set of electrical conductors, often on a backplane, that carry data and power signals among the various components of a computer.

Byte

The group of bits which a computer processes as a unit; often, 8 bits.