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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 10' dyne per cm-' (101 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 principle types are aneroid and mercurial.

Barometric pressure
Same as atmospheric pressure.

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 atmosphere spheric 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.