Glossary and Acronyms: B

Bar:

unit of pressure equal to 10⁵ Pascals.

Barometer:

instrument for measuring atmospheric pressure.
An aneroid barometer is composed of one or series of aneroid capsules. These capsules are thin and disk-shaped boxes, usually metallic, partially evacuated and sealed, held extended by a spring which expands and contracts with changes in atmospheric pressure.
A mercury barometer is an instrument in which the atmospheric pressure is balanced against the pressure exerted by a column of mercury.

Barometric constant:

factor relating the pressure and the height of a column of mercury. 1 hPa = 0,750 062 mm. 1 mm = 1,333 224 hPa.
Barometric corrections are corrections which must be applied to the reading of a mercury barometer in order that the observed value may be accurate.

Barotropic (atmosphere):

model atmosphere in which density is solely a function of pressure and in which the isopycnic surfaces (surface of constant air density).
Tropical atmosphere is almost barotropic. It means the horizontal gradients of temperature and geopotential are weak, in comparison with those in the mid-latitudes (except the tropical systems).

Baroclinic (atmosphere):

model atmosphere in which the isopycnic surfaces (surface of constant air density) intersect the isobaric surfaces (surface of constant pressure).
A baroclinic disturbance (or a baroclinic wave) is a low-pressure system which forms in a region of the atmosphere characterized by a strong horizontal gradient of temperature and a strong thermal wind. Wave disturbances on the polar front are examples of these. Tropical disturbances are not part of these.

Best-Track:

This bulletin gathers the analysed data which detail the structure of a tropical system during its life cycle. These data result from an expertise and a post re-analysis. This bulletin 'best-track' is usually issued by the RSMC in the course of the month following the end of a tropical system which has reached a significant intensity during its life, and respect the format recommended by the WMO.

Beaufort scale:

wind force scale, originally based on the state of the sea, expressed in numbers from 0 to 12. This scale has been imagined by the Admiral Francis Beaufort in 1805. The scale has changed through the years. The Beaufort scale below is the one used internationally since 1946.

Force	Wind (Knots)	WMO Classification	Appearance of Wind Effects
Force	Wind (Knots)	WMO Classification	On Land	On the Water
0	Less than 1	Calm	Calm, smoke rises vertically	Sea surface smooth and mirror-like
1	1-3	Light Air	Scaly ripples, no foam crests	Smoke drift indicates wind direction, still wind vanes
2	4-6	Light Breeze	Wind felt on face, leaves rustle, vanes begin to move	Small wavelets, crests glassy, no breaking
3	7-10	Gentle Breeze	Leaves and small twigs constantly moving, light flags extended	Large wavelets, crests begin to break, scattered whitecaps
4	11-16	Moderate Breeze	Dust, leaves, and loose paper lifted, small tree branches move	Small waves 1-4 ft. becoming longer, numerous whitecaps
5	17-21	Fresh Breeze	Small trees in leaf begin to sway	Moderate waves 4-8 ft taking longer form, many whitecaps, some spray
6	22-27	Strong Breeze	Larger tree branches moving, whistling in wires	Larger waves 8-13 ft, whitecaps common, more spray
7	28-33	Near Gale	Whole trees moving, resistance felt walking against wind	Sea heaps up, waves 13-20 ft, white foam streaks off breakers
8	34-40	Gale	Whole trees in motion, resistance felt walking against wind	Moderately high (13-20 ft) waves of greater length, edges of crests begin to break into spindrift, foam blown in streaks
9	41-47	Strong Gale	Slight structural damage occurs, slate blows off roofs	High waves (20 ft), sea begins to roll, dense streaks of foam, spray may reduce visibility
10	48-55	Storm	Seldom experienced on land, trees broken or uprooted, "considerable structural damage"	Very high waves (20-30 ft) with overhanging crests, sea white with densely blown foam, heavy rolling, lowered visibility
11	56-63	Violent Storm		Exceptionally high (30-45 ft) waves, foam patches cover sea, visibility more reduced
12	64+	Hurricane		Air filled with foam, waves over 45 ft, sea completely white with driving spray, visibility greatly reduced

Beta (effect):

Variation of the Coriolis parameter with latitude.

BF:

Banding Feature. Acronym used for the analysis of a tropical system with the Dvorak Technique.

BoM :

Australian Bureau of Meteorology. (http://www.bom.gov.au/).

Buoy (drifting):

untethered ocean buoy equipped with meteorological and/or oceanographic sensing instrument linked to transmitting equipment for sending the observed data to collecting centers.