Thursday, 19 April 2018
Champions DEFGH (Sawgrass Marriott)
Dual-polarization radar observations were taken of Hurricane Arthur prior to and during landfall, providing needed insight into the microphysics of tropical cyclone precipitation. 30 hours of data were composited and analyzed by annuli capturing storm features (eyewall, inner rainbands, and outer rainbands) and by azimuth relative to the deep-layer environmental wind shear vector. Polarimetric radar variables displayed distinct signatures of convective and stratiform precipitation which were organized in a manner consistent with the expected kinematic asymmetry of a sheared tropical cyclone. Vertical profiles of differential reflectivity (ZDR) and the co-polar correlation coefficient (ρHV) exhibited an expected ZDR maximum and ρHV minimum within the melting layer. In the right-of-shear half, the ZDR and ρHV local extrema were vertically-stretched, rounded bumps between 3-8 km altitude, which are attributed to convective precipitation processes. In the left-of-shear half, the extrema within the melting layer were pointed peaks which are attributed to stratiform precipitation processes. In the outer rainbands, an analysis of normalized propagation differential phase shift (ΦDP) indicated that nonspherical ice particles had an increased presence in the downshear-right quadrant in the layer just above the melting level. Here, convective updrafts generated these ice particles, likely columnar crystals, and increased local diversity of hydrometeor shapes. A sharp transition in hydrometeor population occurred downwind in the downshear-left quadrant where ice column counts and shape diversity were reduced owing to aggregation in a predominantly stratiform regime. The eyewall quadrants did not exhibit such a sharp transition in signatures owing to stronger winds and shorter distances which enhanced azimuthal transport of ice hydrometeors.
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