The Use of Radial Velocity Derivative to Diagnose Rotation and Divergence

Traditional methods of calculating rotational and divergent shears from Doppler radial velocity data can give results that vary widely from the true value of shear for the meteorological feature being sampled. Some factors that must be considered include noisy data, the azimuthal offset of sample volumes from the center of the feature (Wood and Brown 1997), and the radar viewing angle. One commonly used technique relies simply on the difference of the maximum and minimum radial velocity within a rotation or divergence feature. This method is plagued with uncertainties in the values of the shear estimates as well in locating the center of a shear feature. This work illustrates results from a two-dimensional, local, linear least squares (LLSD) method to minimize the large variances in rotational and divergent shear calculations.