Brief communication: A note on the variance of wind speed and turbulence intensity

Abstract. This paper addresses the issue that several papers in the peer-reviewed literature on wind energy applications have used an incorrect equation that equals the variance of wind speed (σU2) to the sum of the variances of the wind components. This incorrect equation is often used to calculate turbulence intensity (TI), which, as a consequence, is often incorrectly estimated too. While exact analytical equations do not exist, here two approximate analytical equations are derived for σU2 and TI as functions of the variances and means of the wind components. Both formulations are validated with samples from a prior field campaign and perform satisfactorily.