Friday, 8 August 2003
Classification and Characterization of Tropical Precipitation Based on High-Resolution Airborne Vertical-Incidence Radar
High-altitude airborne measurements of vertical incidence radar reflectivity and radial velocity are analyzed for some 21,231 km of flight tracks over tropical precipitation systems. A technique based on that used for TRMM (Tropical Rainfall Measurement Mission) reflectivity profiles is used to contrast convective hydrometeor profiles against stratiform ones. The strength of the radar dataset lies in its superb vertical resolution, sufficient to unambiguously detect a bright band, which defines stratiform precipitation. Key findings are that the vertical resolution of the TRMM radar is generally sufficient to detect stratiform rain at nadir, and that the instantaneous hydrometeor vertical motion profile cannot be used to discriminate convective from stratiform rain. The vertical incidence radar reflectivity and Doppler velocity data are then combined with coincident upwelling 85 GHz radiances to analyze and compare convective and stratiform precipitation in several Atlantic tropical cyclones and smaller tropical precipitation systems in Central Florida and in Amazonia. The emphasis of this comparison is on the difference between the oceanic and continental systems. Tropical depressions and cyclones are found to be largely and robustly stratiform, displaying a remarkably narrow echo and vertical velocity spectrum. Florida thunderstorms produce little stratiform precipitation but extensive anvils. Their spectrum of echo and updraft strengths is broad, including some of the highest reflectivities aloft, resulting in very low 85 GHz radiances. And Amazonian precipitation systems are rather weak and more maritime in echo, vertical velocity, and ice scattering characteristics, compared to those in Florida.