Polarimetric Radar Observations of the Persistently Asymmetric Structure of Tropical Cyclone Ingrid

Abstract

Tropical Cyclone Ingrid had a distinctly asymmetric reflectivity structure with an offshore maximum as it passed parallel to and over an extended coastline near a polarimetric weather radar located near Darwin, northern Australia. For the first time in a tropical cyclone, polarimetric weather radar microphysical analyses are used to identify extensive graupel and rain?hail mixtures in the eyewall. The overall microphysical structure was similar to that seen in some other asymmetric storms that have been sampled by research aircraft. Both environmental shear and the land?sea interface contributed significantly to the asymmetry, but their relative contributions were not determined. The storm also underwent very rapid changes in tangential wind speed as it moved over a narrow region of open ocean between a peninsula and the Tiwi Islands. The time scale for changes of 10 m s?1 was of the order of 1 h. There were also two distinct types of rainbands observed?large-scale principal bands with embedded deep convection and small-scale bands located within 50 km of the eyewall with shallow convective cells.