EXTENDED VELOCITY TRACK DISPLAY (EVTD) - AN IMPROVED PROCESSING METHOD FOR DOPPLER RADAR OBSERVATIONS OF TROPICAL CYCLONES

The authors present an improved version of the velocity track display (VTD) method, proposed by Lee et al., to deduce the primary vortex cir culation in hurricanes from airborne Doppler radar data obtained durin g straight-line legs through the storm center. VTD allows the derivati on of one projection of the mean horizontal wind, the wavenumber 0, 1, and 2 components of the tangential wind and one projection of the rad ial wind, in a series of concentric rings centered on the storm circul ation center. The extended VTD (EVTD) algorithm determines additional information through a combination of data collected during successive legs: the Cartesian components of the mean horizontal wind; the wavenu mber 0, 1, and 2 components of the tangential wind; and the wavenumber 0 and 1 components of the radial wind. Application of EVTD to airborn e Doppler data collected on 17 September 1989 in Hurricane Hugo is dis cussed. Comparisons between the EVTD-derived winds, the flight-level m easurements, and winds deduced from ''pseudo-dual-Doppler'' analyses s how qualitatively good agreement. These results reveal the asymmetric structure of the storm and show that it was in a deepening stage, with increasing tangential wind, inflow, and upward velocity. Further appl ications are finally discussed.