Spatial Structure of Fluctuating Components of the Horizontal Wind Speed Above the Ocean

Abstract

Cross correlations of horizontal wind fluctuations between points separated in space were measured at the Marine Observation Tower with a network of three-dimensionally distributed cup-anemometers.The phase shift of wind fluctuations between vertically separated points, and the coherence of wind fluctuations between points arranged in vertical, lateral and longitudinal directions were calculated. The vertical, lateral and longitudinal sizes of the turbulent eddy were empirically formulated in terms of the vertical, lateral and longitudinal coherences, respectively. A model of three-dimensional structure of horizontal wind components is represented by a distorted cylindrical form.Taylor's hypothesis of frozen turbulence is confirmed to hold for every frequency (0.01 Hz<n<0.5 Hz).

Some Features of the Spatial Structures of the Surface Layer Turbulence in the High Wind Condition

“…4 The same as Fig. 1 From k*, k*' is obtained and is compared with Naito and Kondo's (1974) result as also shown in Fig. 5.…”

“…The experimental formula commonly used for the coherence of the velocity fluctuations between two points is where U is mean wind velocity at the observation level and k* is a decay factor, which is usually treated as a constant except for Naito and Kondo's (1974) paper. Shiotani and Iwatani (1971) and Naito and Kondo (1974) used the mean wind velocity U1 at the height of 10m in place of U. Then, equation (9) is written as follows;…”

“…According to Naito and Kondo (1974), the decay factor k*' is given by As the cospectrum Co(*, *; n) is an even function of frequency n and the quadrature spectrum Q(*, *; n) is an odd function, we have from (2) And also, from (4) and (5), we have where ko and p are the constants, and z is a height of the observation level. Equation (10) implies that the decay factor k*' is nearly equal to ko when **z and then, Naito and Kondo's (1974) result agrees almost with others'.…”

“…Although Naito and Kondo (1974) show that the decay factor k* is constant, Powell and Flderkin (1974) state that for larger separation distances the factor becomes larger, and Panofsky and Mizuno (1975) show a linear relation to the separation distance. The coherence and the phase are computed from Narashino wind data.…”

“…For instance, the decay factor has been usually treated as a constant, but Naito and Kondo (1974) show that it should be treated as a function of separation distance. Magnitudes of decay factors, therefore, are uncertain as there is not sufficient basic data.…”