DICTIONARY OF AVIATION 267
zenithal 'zii-ni-Oal adj. of the zenith.
zenith-distance 'zii-ni0,distns n. the angular distance of any bedy from the zenith or vertex of the hevens; the arc or portion of a great circle of the hevens intercepted be- tiueen the zenith and any object in the sky; the cosaltitude.
Zeppelin 'zepa-hn . a dirigible balloon of the type devel- opt by Ferdinand von Zeppelin; a Zeppelin airship.
zone zoon n. a belt or band; specifically, one of the five arbitrary divisions of the earth's surface, bounded by lines parallel to the equator; a climatic belt: as, the -torrid *zone, or one of the temperate or frigid *zones; also, any horizon- tal or vertical belt, tjact, or region, as of the atmosfere, differing in character from adjoining belts : as, a *zone of discontinuity.
climatic zone, one of the zones, belts, or tjacts girdling the earth and characterized by certain climatic conditions; one of a number of elongated or beltzlike subdivisions of the surface of the globe distinguisht by successiv differ- ~nces of climate : as, Koeppen's *climatic zones, Wojei- koff's *climatic zones.
zone of cyclones, the zone or belt between latitudes 30 and 60, characterized by the prevalence of cyclones due to the conflict of descending polar winds with ascending equa- torial winds.
zone of discontinuity, a zone or region of the atmosfere irhere the wind^conditions are discontinuous; the neutjal aerial belt or txact constituting the meeting^place of the rising air^currents and the upper^wind; an upper inversions zone; a calmszone.
zone of equilibrium, a zone, t^act, stratum, or layer of the atmosfere in tuhich a balloon assumes a condition of equi- librium, equipoise, balance, or stability, tending neither to rise nor fall.
zone of mixture, a zone characterized by the mixture of conflicting winds, such as a zone of cyclones.
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