probability distribution of a variable over a long time scale
NOTE The time scale exceeds the duration of a sea state, in which the statistics are assumed constant (see short-term distribution in 3.29). The time scale is hence comparable to a season or to the design service life of a structure.
EXAMPLE Long-term distributions of
⎯ significant wave height,
⎯ significant wave height in the months May to September,
⎯ individual wave heights,
⎯ current speeds (such as for the vortex induced vibrations of drilling risers),
⎯ scatter diagrams with the joint distribution of significant wave height and wave period (such as for a fatigue analysis), or ⎯ a particular action effect.
Source: API RP 2MET, Derivation of Metocean Design and Operating Conditions, First Edition, November 2014. Global Standards