Science / Weather Glossary

Backscatter: A radar echo that is reflected, or scattered, at 180 degrees to the direction of the incident wave. Also the scattering of radiant energy into space before it reaches the earth's surface.

Ball Lightning: A relatively rare form of lightning consisting of a luminous ball, often reddish in color, which moves rapidly along solid objects or remains floating in mid-air.

Baroclinity: The state of stratification in a fluid in which surfaces of constant pressure intersect surfaces of constant density. Also known as baroclinicity. An example is the tight temperature gradien . . . View Full Definition

Barograph: An instrument that continuously records a barometer's reading of atmospheric pressure.

Barometer: An instrument used to measure atmospheric pressure. Two examples are the aneroid barometer and the mercurial barometer.

Barometric Pressure: The pressure exerted by the atmosphere at a given point. Its measurement can be expressed in several ways. One is in millibars. Another is in inches or millimeters of mercury (Hg).

Barotropy: The state of a fluid in which surfaces of constant density or temperature are coincident with surfaces of constant pressure. It is considered zero baroclinity.

Barrier Winds: Refers to the westerly flow of air along the northern slope of the Brooks Range in northern Alaska that precedes the arrival of colder air from the north.

Bathythermograph: A device used to obtain a record of temperature against depth (pressure) in the ocean. May be referred to as a B.T.

Beaufort Wind Scale: A system of estimating and reporting wind speeds. It is based on the Beaufort Force or Number, which is composed of the wind speed, a descriptive term, and the visible effects upon land obje . . . View Full Definition

Bellot Winds: Refers to the winds in the Canadian Arctic that blow through the narrow Bellot Strait between Somerset Island and the Boothia Peninsula, connecting the Gulf of Boothia and Franklin Strait.

Bermuda High: A semi-permanent, subtropical area of high pressure in the North Atlantic Ocean that migrates east and west with varying central pressure. Depending on the season, it has different names. Wh . . . View Full Definition

Bernoullis Theorem: A statement of the conservation of energy for a steady, nonviscous, incompressible level flow. It is an inverse relationship in which pressures are least where velocities are greatest. Theor . . . View Full Definition

Biosphere: The transition zone between the earth and the atmosphere within which most terrestrial life forms are found. It is considered the outer portion of the geosphere and the inner or lower portio . . . View Full Definition

Black Blizzard: A local term for a violent duststorm on the south-central Great Plains that darkens the sky and casts a pall over the land.

Black Ice: Thin, new ice on fresh or salt water that appears dark in color because of its transparency. Also refers to thin, transparent ice on road surfaces.

Blizzard: A severe weather condition characterized by low temperatures, winds 35 mph or greater, and sufficient falling and/or blowing snow in the air to frequently reduce visibility to 1/4 mile or le . . . View Full Definition

Blocking High: The development of a warm ridge or cutoff high aloft at high latitudes which becomes associated with a cold high at the surface, causing a split in the westerly winds. Such a high will move . . . View Full Definition

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