Okta

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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.