Simulated Doppler Velocity Signatures of Evolving Tornado-Like Vortices

Abstract

Doppler radar observations have revealed a class of atmospheric vorti-ces (tropical cyclones, tornadoes, dust devils) that possess elliptical radar reflectivity signatures. One famous example is Typhoon Herb (1996) that maintained its elliptical reflectivity structure over a 40-hour period. Theoretical work and dual-Doppler analyses of observed tropical cyclones have suggested two physical mechanisms that can explain the formation of two types of elliptical vortices observed in nature, namely, the combination of a circular vortex with either a wavenumber two vortex Rossby wave or a deformation field. The characteristics of these two types of elliptical vorti-ces and their corresponding Doppler velocity signatures have not been previously examined. Idealized elliptical vortices consisting of a Rankine vortex combined with wavenumber two disturbances are constructed and sampled by a hypothetical Doppler radar. The Doppler velocity patterns of all wavenumber two cases shown in this study are visually similar. The characteristics of the two-dimensional flow patterns and the corresponding Doppler velocities produced by an idealized vortex Rossby wave and deformation field are illustrated. The ground-based velocity track display (GBVTD) single Dop-pler vortex wind retrieval technique was performed on these two types of elliptical vortices. The GBVTD technique can retrieve wavenumber two components in the vortex Rossby wave case outside the RMW but failed to retrieve wavenumber two structure of the deformation case for all radii. It TAO, Vol. 17, No. 2, June 2006 430 can be seen that when the phase of the wavenumber two V T is ahead of V R by π/4 with same amplitude, GBVTD coefficients A3 and B3 are near zero; hence, GBVTD technique cannot retrieve the wavenumber two amplitude in these conditions. However, by knowing the elliptical shape of the vortex as a priori these two mechanisms can still be distinguished by the characteristics of the corresponding GBVTD coefficients.

Analysis of Pressure Distribution on a Single-Family Building Caused by Standard and Heavy Winds Based on a Numerical Approach

“…It was assumed that the cross-section of the wind tunnel was crucial for the correct analysis of the results; therefore, its parameters (hereinafter referred to as boundary conditions) were checked in detail, and the stress values were compared. To accurately compare the results depending on the boundary conditions, the stress reading locations have been changed, and their [31,32] The study involved creating a wind tunnel model, initially in the shape of a horizontal cylinder, in which one of the circular bases was modeled as an air inlet while the opposite one was modeled as an outlet. A model of the analyzed building was placed centrally in the tunnel.…”

“…The general analysis scheme, along with the first assumptions, is presented in Figure 4. [31,32] The study involved creating a wind tunnel model, initially in the shape of a horizontal cylinder, in which one of the circular bases was modeled as an air inlet while the opposite one was modeled as an outlet. A model of the analyzed building was placed centrally in the tunnel.…”

LIDAR ground-based velocity track display analyses and surface observations of a vortex shedding event observed at the Hong Kong International Airport on April 11, 2011

“…Parameters V 0 and R for V1 and V2 are calculated from LIDAR measurements at the lowest sweep (z ~260 masl), V 0 varies in time for each vortex and R is set equal to the mean core radius of each, which is 480 m (R is constant rather than varying in time owing to uncertainties in its measurement using LIDAR observations). K = 1.2564, a theoretical value calculated by Davies-Jones and Wood (2006) and adopted in Wood and Brown (2011). Observations of vortex position and V 0 are interpolated via a polynomial fit at 10-s intervals to facilitate calculations at time steps between LIDAR sweeps (the polynomial fit to the positions of V1 and V2 used in these models are shown in Fig.…”

A review of convective and artificial vortices for power generation

“…Davies-Jones and Wood [34] utilized exact solutions of the Navier-Stokes or Euler equations of motion and the continuity equation in cylindrical coordinates for 3D, axisymmetric, inviscid, or laminar flows to represent evolving vortices that roughly model tornado cyclones or misocyclones contracting to tornadoes. These solutions are unsteady versions of the diffusive Burgers-Rott vortex and the inviscid Rankine-combined vortex.…”