VELOCITY TRACK DISPLAY - A TECHNIQUE TO EXTRACT REAL-TIME TROPICAL CYCLONE CIRCULATIONS USING A SINGLE AIRBORNE DOPPLER RADAR

The concept and formulation of a real-time airborne Doppler radar wind field analysis technique, velocity track display (VTD), is presented. The VTD algorithm is a harmonic analysis method similar to the veloci ty-azimuth display technique for ground-based radar; however, it is de signed to deduce the primary circulation properties of atmospheric vor tices such as tropical cyclones. When an aircraft, equipped with a Dop pler radar scanning in a track-orthogonal plane, penetrates a cyclonic circulation. VTD decomposes Doppler velocities on cylindrical rings i nto tangential, radial, and the mean cross-track component of the wind velocity. Obtaining estimates of the vortex circulation requires data from only one aircraft flight leg instead of two in the pseudodual Do ppler radar method. As a test, the VTD technique was applied to two or thogonal legs (''figure 4'' pattern) in Hurricane Gloria (1985). The e ntire computation was completed about 15 min after the end of each fli ght leg with little or no human interaction. The reconstructed hurrica ne vortex structure (the mean tangential wind, mean radial wind, and t he total tangential wind) is consistent with those documented in the l iterature by elaborate techniques that demand extensively interactive decisions and intensive computations. The output consists of about 400 0 Fourier coefficients, which can be transmitted from an aircraft to a forecast center via geosynchronous satellite link in real-time for fu rther analysis and as initialization for tropical cyclone models. A ve rsion of VTD was run successfully on board a NOAA WP-3D during the 199 1 hurricane season.