| Section A | A index | 621-629 of 917 terms |
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antiproton—The proton's antiparticle, first observed in 1955.
Chamberlain, O., E. Segrè, C. Wiegand, and T. Ypsilantis, 1955: Phys. Rev., 100, 947–950.
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antisolar point—The point on the celestial sphere that lies directly opposite the sun from the observer, that is, on the line from the sun through the observer.
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antitrades—A deep layer of westerly winds in the troposphere above the surface trade winds of the Tropics. They comprise the equatorward side of the midlatitude westerlies, but are found at upper levels rather than at the surface. The antitrades are best developed in the winter hemisphere and also above the eastern extremities of the subtropical highs. Farther west their base is higher and their appearance less regular. The antitrades were formerly regarded as return currents carrying away, to higher latitudes, the air that rises in the intertropical convergence zones, the westerly component being due to the conservation of angular momentum as the air moves into higher latitudes. Bjerknes (1935) showed that this explanation is incomplete: The antitrades are dynamical in origin and constitute an essential part of the atmosphere's primary circulation.
Bjerknes, J., 1935: La circulation atmosphérique dans les latitudes sous-tropicales. Scientia, 57, 114–123.
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antitwilight arch—A bright wedge of pink, orange, or purple light that extends around the antisolar horizon during clear twilights and that has the greatest vertical width (∼3°–6°) occurring above the antisolar point. The antitwilight arch rises with the antisolar point at sunset and sets with the antisolar point at sunrise. The antitwilight arch is brighter than the bluish gray dark segment beneath it. The boundary between these features may be distinct shortly after sunset (sun elevation h0 ∼ −2°), but it fades as evening twilight progresses.
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anvil cloud—The anvil-shaped cloud that comprises the upper portion of mature cumulonimbus clouds; the popular name given to a cumulonimbus capillatus cloud, particularly if it embodies the supplementary feature incus (from the Latin for anvil).
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apaapaa—In Hawaii, a high gale.
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