Measure of the variance associated with the fluctuating wind speed per unit frequency band.
NOTE 1 The wind spectrum is an expression of the dynamic properties of the wind (turbulence). It reflects the fluctuations about and in the same direction as a certain mean wind speed, usually the 1 h sustained wind speed. There is hence no direction variable associated with the wind spectrum within this document.
NOTE 2 As the sustained wind speed varies with elevation, the wind spectrum is a function of elevation.
Source: API RP 2MET, Derivation of Metocean Design and Operating Conditions, First Edition, November 2014. Global Standards