Handout (319.2 kB)
In an attempt to determine the degrees of varying tangential wind profiles in atmospheric vortices, a new analytical model is presented. The model employs four parameters: maximum tangential wind (Vx), core radius (Rx) at which maximum tangential wind occurs, k which controls the concavity of the tangential velocity profile near the vortex center, and n which controls the decay rate of the profile (i.e., rate at which tangential velocity decays with increasing radial distance, r, outside the core). When k is less than or equal to 0.5, the tangential velocity profile near the vortex center has negative curvature (curve turns to right with increasing r) and a local vertical vorticity is maximum at the center, suggestive of a one-celled vortex. When k > 0.5, the profile has positive curvature (curve turns to left) near the center and an annulus of maximum vorticity is formed while being displaced away from the center toward the strongest gradient of the profile inside the core radius, consistent with a two-celled vortex. When n (which always exceeds k) is small, the tangential velocity profile outside the core radius is nearly flat (i.e., small decay rate). Increasing the n values increases the decay rate.
Least squares fits of four model parameters to Doppler-analyzed and -derived tangential wind profiles provide evaluation of the parameters' distributions and critical examination of the profile's realism. Mobile, high-resolution Doppler radar measurements of the 15 May 1999 Stockton, Kansas and 30 May 1998 Spencer, South Dakota tornadoes are used to test against the fitted parameters of the analytical model.
Comparison of the fitted wind profiles and those analyzed or derived from Doppler radar observations shows good agreements. The results will be presented at the Conference.