Wide Slow-Moving Rainbands and Narrow Fast-Moving Rainbands Observed in Typhoon 8913

Abstract

The size, motion, and structure of the rainbands in Typhoon 8913 are presented from observations using a long-range conventional radar and two Döppler radars. These rainbands were classified into wide slow-moving and narrow fast-moving. Wide (50-150km) rainbands have a small angular velocity (≤10°h^-1) and a long lifetime (6-10h or more). Narrow (25-50km) rainbands are generated in a region more upwind and inward than wide rainbands every 3-4h. They rotate cyclonically around the typhoon center at a large angular velocity (30°h^-1) during their short lifetime (1-4h), and catch up and merge with wide rainbands. One wide slow-moving rainband is accompanied with a disturbance (convergence, updraft, and high vorticity) inclining outward with a large slope (1/10) on its inside. One narrow fast-moving rainband is associated with a nearly upright disturbance. The structure of the disturbance differs, however, from the inertia-buoyancy waves proposed in some previous studies as the mechanism behind fast-moving rainbands. Both types of rainbands are characterized by stratiform precipitation in which low-level shallow convective cells are embedded, and make no cold pools in the boundary layer.