Meso-.ALPHA.-Scale Wind Field and Precipitating Clouds in Typhoon 9426 (Orchid) Observed by the MU Radar

Abstract

A general structure of Typhoon 9426 (Orchid) up to the lower stratosphere including the inner core region was observed by the MU (middle and upper atmosphere) radar on 29-30 September 1994. In this paper, a meso-α-scale wind field and meso-β and -y scale features of precipitating clouds in the typhoon were investigated. The kinematic structure in the front and rear of the typhoon was quite different because of its transition from mature to decaying stages and an asymmetric distribution of cloud and precipitation. In front of the typhoon, the meso-α-scale wind field was characterized by a cyclonic rotation with the maximum at low level, outflow regions tilted outward with height, and vertical motions affected by convection and topography. In the vicinity of the typhoon center, the tangential wind had a vertical spiral structure for the center, considered to be the result from deformation of the center of the decaying typhoon. In the rear of the typhoon without precipitating clouds, the cyclonic wind became weak, and the outflows and vertical motions as seen in the front were not detected. In front of the typhoon, an eyewall and wide rainband were observed. In the eyewall, a meso-γ-scale remarkable updraft associated with an outflow region, considered to be a part of vertical circulation, was found in the upper troposhere. The outflow region tilted outward was originated from the area of maximum radial shear of the low-level cyclonic wind. It was extended to an updraft region within an upper-level band-shaped cloud, located far from the typhoon center. The wide rainband (50-70 km width) was located at the outer edge of the band-shaped cloud, and it lasted in the development of the upper-level cloud. It was accompanied by the tilted outflow region to 6 km altitude, the bottom of which was located at the maximum of the cyclonic wind. A narrow rainband (20-40 km width), that a lifetime was quite short (1.5 hours), was also observed by the boundary layer radar (BLR) at another site. An outflow region with the tilted structure was present in the outer part (convective portion) of the rainband, and its bottom was not associated with strong cyclonic wind as seen in the wide rainband.