AskDefine | Define okta

User Contributed Dictionary

English

Alternative spellings

Noun

  1. One eighth of the total area of the celestial dome; used as a measure of cloudiness (one okta means that one eighth of the sky is obscured, two oktas that one quarter is obscured, and so on).
    • 1960, American Meteorological Society, Meteorological and Geoastrophysical Abstracts, American Meteorological Society, Page 480
      ...64% of the low- and 50% of the high-cloud amount differences were within ± 1 okta, although many of these successes (71% in the low-cloud amount) were for cases of totally clear or totally cloudy skies.
    • 1985, University of East Anglia, Geo Abstracts, University of East Anglia, Page 29
      Mean cloud amount distributions are transformed to normal distributions. The accuracy of the method is indicated by the retrieval of the original distribution with a typical error of 14% in the frequency of each okta of cloud amount. - Author
    • 2001, W.G. Rees, Physical Principles of Remote Sensing - Second Edition, Cambridge University Press, Page 100
      For example, it has been estimated that a Landsat satellite, which revisits a particular location once every 16 days, will obtain a cloud-free scene of a particular location in Britain only once per year, and a scene with 1 okta of cloud (an okta is one eighth of the sky obscured by cloud) only twice per year.

Translations

  • Finnish: kahdeksasosa

Northern Sami

Cardinal number

okta

Extensive Definition

In meteorology, an okta is a unit of measurement used to describe cloud cover. Sky conditions are estimated in terms of how many eighths of the sky are obscured by cloud, ranging from completely clear, 0 oktas, through to completely overcast, 8 oktas. In addition in the SYNOP code there is cloud cover indicator '9' indicating that the sky is obscured, usually due to dense fog or heavy snow.
Although relatively straightforward to measure (for instance, by using a mirror), because it estimates cloud cover simply in terms of the area of the sky obscured by clouds, it does not account for cloud type or thickness. This limits its use for estimating cloud albedo or surface solar radiation receipt.oktas are rare.

References

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