Velocity Track Display—A Technique to Extract Real-Time Tropical Cyclone Circulations Using a Single Airborne Doppler Radar

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  • 1 National Center for Atmospheric Research, Boulder, Colorado
  • | 2 Hurricane Research Division, NOAA/AOML, Miami, Florida
  • | 3 National Center for Atmospheric Research, Boulder, Colorado
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Abstract

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 velocity–azimuth display technique for ground-based radars; however, it is designed to deduce the primary circulation properties of atmospheric vortices such as tropical cyclones. When an aircraft, equipped with a Doppler radar scanning in a track-orthogonal plane, penetrates a cyclonic circulation, VTD decomposes Doppler velocities on cylindrical rings into 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 pseudo-dual Doppler radar method.

As a test, the VTD technique was applied to two orthogonal legs (“figure 4” pattern) in Hurricane Gloria (1985). The entire computation was completed about 15 min after the end of each flight leg with little or no human interaction. The reconstructed hurricane vortex structure (the mean tangential wind, mean radial wind, and the total tangential wind) is consistent with those documented in the literature by elaborate techniques that demand extensively interactive decisions and intensive computations. The output consists of about 4000 Fourier coefficients, which can be transmitted from an aircraft to a forecast center via geosynchronous satellite link in real-time for further analysis and as initialization for tropical cyclone models. A version of VTD was run successfully on board a NOAA WP-3D during the 1991 hurricane season.

Abstract

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 velocity–azimuth display technique for ground-based radars; however, it is designed to deduce the primary circulation properties of atmospheric vortices such as tropical cyclones. When an aircraft, equipped with a Doppler radar scanning in a track-orthogonal plane, penetrates a cyclonic circulation, VTD decomposes Doppler velocities on cylindrical rings into 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 pseudo-dual Doppler radar method.

As a test, the VTD technique was applied to two orthogonal legs (“figure 4” pattern) in Hurricane Gloria (1985). The entire computation was completed about 15 min after the end of each flight leg with little or no human interaction. The reconstructed hurricane vortex structure (the mean tangential wind, mean radial wind, and the total tangential wind) is consistent with those documented in the literature by elaborate techniques that demand extensively interactive decisions and intensive computations. The output consists of about 4000 Fourier coefficients, which can be transmitted from an aircraft to a forecast center via geosynchronous satellite link in real-time for further analysis and as initialization for tropical cyclone models. A version of VTD was run successfully on board a NOAA WP-3D during the 1991 hurricane season.

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