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- Author or Editor: Yukihiro Mori x
- Journal of Applied Meteorology and Climatology x
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Abstract
In a recent paid, the author reviewed methods for estimating the mean and the standard deviation of wind direction. Some comments on this subject are now added. If large sporadic eddy fluctuations do not occur in a sampling duration, we can exactly calculate an arithmetic mean and standard deviation of wind direction by using an approach suggested by Mitsuta. This is via a single-pass procedure without considering the discontinuity in wind direction scale. By using the Mitsuta approach it is found that Mardia's method provides a good estimator of the standard deviation of wind direction even in the case when the range of fluctuations of wind direction is wide.
Abstract
In a recent paid, the author reviewed methods for estimating the mean and the standard deviation of wind direction. Some comments on this subject are now added. If large sporadic eddy fluctuations do not occur in a sampling duration, we can exactly calculate an arithmetic mean and standard deviation of wind direction by using an approach suggested by Mitsuta. This is via a single-pass procedure without considering the discontinuity in wind direction scale. By using the Mitsuta approach it is found that Mardia's method provides a good estimator of the standard deviation of wind direction even in the case when the range of fluctuations of wind direction is wide.
Abstract
Proposed single-pass methods for estimating the mean (D̄) and the standard deviation (σ d ) 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 D̄ and σ d provide good estimators in practical application. Yamartino's empirical method also provides a good estimator of σ d .
The relationship between the vector mean wind speed Vv and the scalar mean wind speed Va has been investigated in connection with σ d and the standard deviation of the crosswind velocity σ v . It is found that Kampé de Fériet-Frenkiel's equation, which represents the relation for Vv and Va in terms of σ v , holds for the field data, so we can get an estmator of σ v 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(−0.5σ d 2) for σ d <20 deg.
Abstract
Proposed single-pass methods for estimating the mean (D̄) and the standard deviation (σ d ) 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 D̄ and σ d provide good estimators in practical application. Yamartino's empirical method also provides a good estimator of σ d .
The relationship between the vector mean wind speed Vv and the scalar mean wind speed Va has been investigated in connection with σ d and the standard deviation of the crosswind velocity σ v . It is found that Kampé de Fériet-Frenkiel's equation, which represents the relation for Vv and Va in terms of σ v , holds for the field data, so we can get an estmator of σ v 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(−0.5σ d 2) for σ d <20 deg.
