Application Of Two VAD Methods And VAD Analysis Of Nonlinear Wind Field

In this paper, two Velocity-Azimuth Display (VAD) methods, which are Thomas' and Rabin's, a ss, are presented. Both of them can be applied to retrieve the subsy-scale average wind speed and direction with the least squares solution to the harmonics of the unequally sampled data field. Thomas method is applied to linear wind which includes the second harmonic. But, in the wind field including zero and the first harmonics, Rabin method needs the smaller effective sample area than Thomas method. We require the respective effective sample areas of two VAD methods and analysis their errors. Computing the Doppler actual velocity data shows that, in the effective sample areas, the retrieve values such as average wing speed and direction are much the same as the values of the actual observation.If the actual wind is nonlinear, being different from the linear wind , the convention VAD analysis can not provide directly the mean divergence, the mean deformation, the mean horizontal wind or the components of the wind at the center of the scanned circle. For the general form of a nonlinear wind, the VAD analysis was considered. It includes testing of nonlinear of observations, determine the nonlinear model ( range depends of the F coefficients),and using the least-squares fit in range to obtain the components of the wind. The case analysis of single-Doppler observations shows that the deviation of the result is to the standard of linear wind observations at the same height and time . These developed VAD method is reasonable to the nonlinear wind.