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ABSTRACT
Ten years of data from the Tropical Rainfall Measurement Mission satellite's Precipitation Radar (TRMM PR) show the vertical structure of tropical cyclone rainbands. Radar-echo statistics show that rainbands have a two-layered structure, with distinct modes separated by the melting layer. The ice layer is a combination of particles imported from the eyewall and ice leftaloftas convective cells collapse. This layering is most pronounced in the inner region of the storm, and the layering is enhanced by storm strength. The inner-region rainbands are vertically confined by outflow from the eyewall but nevertheless are a combination of strong embedded convective cells and robust stratiform precipitation, both of which become more pronounced in stronger cyclones.
Changes in rainband coverage, vertical structure, and the amount of active convection indicate a change in the nature of rainbands between the regions inward and outward of a radius of approximately 200 km. Beyond this radius, rainbands consist of more sparsely distributed precipitation that is more convective in nature than that of the inner-region rainbands, and the outer-region rainband structures are relatively insensitive to changes in storm intensity. The rainbands in both inner and outer regions are organized with respect to the environmental wind shear vector. The right-of-shear quadrants contain newer convection while in the left-ofshear quadrants the radar echoes are predominantly stratiform. This asymmetric distribution of rainband structures strengthens with environmental wind shear. Cool sea surfaces discourage rainband convection uniformly.
1. Introduction
Precipitation bands of varying size and extent typically spiral inward toward the center of a mature tropical cyclone. The most prominent of these rainbands, known as the principal rainband, makes up most of the ''stationary band complex'' (Willoughby et al. 1984; Willoughby 1988; Houze 2010), named for the complex's tendency to remain in the same place relative to the translating storm center. The remainder of the stationary band complex consists of smaller secondary bands in the inner core that are often found radially inward of the principal band, and loosely organized convection that forms the distant rainbands in the storm's environment (Houze 2010). These studies emphasize the horizontal distributions of rainbands, but information is needed on their vertical structures to understand their dynamical roles.
Case studies have noted certain features of the vertical structure and dynamics of rainbands....