Estimating vortex center locations and movements in four-dimensional space from radar observed tornadic mesocyclones

A multi-step method is developed to estimate the vortex center locations and movements in four-dimensional space from radar observed tornadic mesocyclones. First, the mesocyclone area is identified as a by-product of the mesocyclone-targeted radar velocity dealiasing on each tilt of radar scan. Then, a two-step algorithm is applied to the dealiased radial-velocity field in the mesocyclone area to estimate the vortex center location on each tilt of each volume scan. Finally, the mesocyclone vortex center location is estimated as a continuous function of height and time by fitting a smooth-function form constructed by B-spline basis functions to the vortex center locations estimated in the second step, and then the tornado vortex center location is estimated as a deviation from the mesocyclone vortex center by fitting a sinusoidal-function form to the residuals of the B-spline fitting. The method is applied to the tornadic mesocyclone observed by operational radars in Oklahoma on 20 May 2013. The results show that the B-spline fitting can capture the mesocyclone vortex center location and movement, while the sinusoidal-function fitting may capture to a certain extent the circular movement of tornado as a satellite vortex around the mesocyclone center within the mesocyclone.