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Mauna Kea Weather Center Meteorology Glossary/Dictionary

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  • ob - In meteorology, a commonly used abbreviation for weather observation.

  • observation - See weather observation.

  • ocean - 1. The intercommunicating body of saltwater occupying the depressions of the earth's surface. 2. One of the major primary subdivisions of the above, bounded by continents, the equator, and other imaginary lines. See sea.

  • octa - A fraction equal to one-eighth of the celestial dome, used in the coding of cloud amounts in synoptic meteorological observations.

  • oe - A violent whirlwind of the Faeroe Island region (north of the British Isles).

  • OLS - Abbreviation for Operational Linescan System.

  • ora - (Also spelled aura.) A regular valley wind at Lake Garda in Italy. See also suer.

  • orographic - Relating to mountains and mountain effects. Often refers to influences of mountains or mountain ranges on airflow, but also used to describe effects on other meteorological quantities such as temperature, humidity, or precipitation distribution. A major effect is orographic lifting.

  • orographic lifting - Ascending air flow caused by mountains. Mechanisms that produce the lifting fall into two broad categories: 1) the upward deflection of horizontal larger-scale flow by the orography acting as an obstacle or barrier; or 2) the daytime heating of mountain surfaces to produce anabatic flow along the slopes and updrafts in the vicinity of the peaks. The first category includes both direct effects, such as forced lifting and vertically propagating waves, and indirect effects, such as upstream blocking and lee waves. Even though this term strictly refers only to lifting by mountains, it is sometimes extended to include effects of hills or long sloping topography. When sufficient moisture is present in the rising air, orographic fog or clouds may form.

  • OSSE - Abbreviation for observing systems simulation experiment.

  • outflow - A current exiting through a strait or passage.

  • outlook - Issued to indicate that a hazardous weather or hydrologic event may develop. It is intended to provide information to those who need considerable lead time to prepare for the event.

  • output - (Or output signal.) The quantity that is delivered by an instrument or a component of an instrument; used in contradistinction to the input.

  • overcast - 1. Descriptive of a sky cover of 1.0 (95% or more) when at least a portion of this amount is attributable to clouds or obscuring phenomena aloft; that is, when the total sky cover is not due entirely to surface-based obscuring phenomena. In aviation weather observations, an overcast sky cover is denoted by the symbol "symbol"; it may be explicitly identified as thin (predominantly transparent); otherwise a predominantly opaque status is implicit. An opaque overcast sky cover always constitutes a ceiling. See obscuration. 2. Popularly, the cloud layer that covers most or all of the sky. It generally suggests a widespread layer of clouds such as that considered typical of a warm front.

  • overturn - (Also called convective overturn.) The mixing of a stratified body of water due to density changes, usually caused by temperature changes.

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