Evaluation of several 'single-pass' estimators of the mean and the standard deviation of wind direction.

Abstract

Proposed single-pass methods for estimating the mean (D) and the standard deviation (sigmad) of wind direction and other problems in wind statistics have been evaluated using extensive field data. It can be concluded that Mardia's methods for estimating D and sigmad provide good estimators in practical application. Yamartino's empirical method also provides a good estimator of sigmad. The relationship between the vector mean wind speed Vv and the scalar mean wind speed Va has been investigated in connection with sigmad and the standard deviation of the crosswind velocity, sigmav. It is found that Kampe de Feriet-Frenkiel's equation, which represents the relation for Vc and Va in terms of sigmav, holds for the field data, so we can get an estimator of sigmav from observed Vv and Va. The ratio of Vv/Va is roughly related to the standard deviation of wind direction, and the relation can be expressed as Vv/Va=exp(-0.5 sigmad2) for sigmad less than 20o.-Author