A Proposed Technique for Diagnosis by Radar of Hurricane Structure

Abstract

A Doppler radar technique is proposed for remote estimation of hurricane structure by sampling the kinematic properties of the hurricane wind field in a relatively small circular area outside the radius of maximum winds. This technique uses Fourier analysis of the pattern of Doppler velocities measured in a horizontal circle surrounding the radar, following guidelines developed by Browning and Wexler. Two indices, potential-vortex fit (PVF) and radial confluence, are developed as measures of the degree of conformity of the wind field sampled by radar to an idealized Rankine axisymmetric cyclone circulation. The PVF index reveals the extent to which the sampled wind held fits a potential-vortex flow regime, wherein both curvature and speed of the tangential wind component are inversely proportional to distance from a circulation center. The confluence of the radial wind component provides an independent estimate of the curvature of the tangential component. These two indices were measured in Hurricane Gloria (1985) during a period of more than 3 h following its landfall. Values of PVF indicated a weakened circulation during the first half of this period, followed in the latter half by a progressive and rapid decay of the circulation, consistent with other observations. The magnitudes of the radial confluence index, on the other hand, evidently were adversely affected by significant contamination by asymmetries in the hurricane circulation throughout most of the observational period. However, trends in both indices provided an early indication of the deterioration of Hurricane Gloria. Accordingly, it appears worthwhile to seek further evidence of the potential value of this technique as an aid in monitoring hurricane severity.