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B-display—A rectangular radar display, with coordinates of azimuth and range, in which targets appear as intensity-modulated blips. Because the shapes of distributed targets are distorted on these coordinates, especially at close range, this type of display is not popular for use in weather radar.
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Babinet point—One of the three commonly detectable points of zero polarization of skylight, neutral points, lying along the vertical circle through the sun; the other two are the Arago point and Brewster point. The Babinet point typically lies only 15° to 20° above the sun, and hence is difficult to observe because of solar glare.The existence of this neutral point was discovered by Babinet in 1840.
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Babinet's principle—An approximation according to which the amplitude of near-forward scattering by an opaque, planar object is the same as that of an aperture of the same shape and size. Babinet's principle is sometimes combined with Fraunhofer diffraction theory in the development of an approximate theory of the corona.
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backdoor cold front—A cold front that leads a cold air mass toward the south and southwest along the Atlantic seaboard of the United States. This is one of the occurrences to which New Englanders give the name sea turn, for the cold wind following a backdoor cold front blows from the northeast quadrant.
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back-sheared anvil—Colloquial expression for a cumulonimbus anvil that spreads upwind into relatively strong winds aloft. A back-sheared anvil implies strong divergent flow near the summit of a high-speed convective storm updraft. These anvils often exhibit a crisp appearance with sharp, distinctive edges.
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background field—In objective analysis and data assimilation, an a priori estimate of the atmospheric state. In most data assimilation systems, the background field is a forecast from the previous analysis time. Note that the term “first-guess field” has been used for the background field, but “background field” is currently the preferred usage.
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