Structure and Evolution of Convection within Typhoon Yancy (T9313) in the Early Developing Stage Observed by the Keifu Maru Radar

[摘要] Typhoon Yancy (T9313), which was in the early gradual developing stage and moved westward over the northwestern Pacific near (19N, 129E), was observed by the Japan Meteorological Agency research vessel Keifu Maru, during 30 August to 1 September 1993. During that period, the circulation center of Yancy approached as close as 80km to the north of the Keifu Maru. Convection in the major part of Yancy was analyzed using the radar, maritime weather and upper air observation data obtained on the ship and recently available satellite data. Cell echo tracking winds (CET winds) were estimated and utilized to supplement low level wind data around Yancy.During the early developing stage, an in-concentric structure of Yancy in which a cloud system existed in a southwest quadrant of a lower-level cyclonic circulation (LLCC) of 1500km scale was transformed to a concentric one through a formation of a central dense overcast (‘CDO’) in the cloud system. After the establishment of the concentric structure, Yancy began rapid development.Various mesoscale (100-500km) precipitation features (MPFs) were organized and evolved successively within Yancy. The configurations of the MPFs were changed as the early developing process progressed through four sub-stages. In the initial sub-stage, a large (400km) echo system (LES) was organized in the southwest quadrant of the LLCC, over which a round cloud system appeared. In the second sub-stage, a long lasting mesoscale intense convective area (MICA) was formed around the northwestern edge of the LES, which was a mesoscale precipitation entity of the ‘CDO’ in the round cloud system. LLCC appeared to be intensified on a 500km scale after the formation of MICA. In the third sub-stage, LES and the cloud system evolved into a comma-shaped spiral band with length over 500km in the intense cyclonic circulation. In the final sub-stage, curvature of the spiral band was increased and an inner near-circular spiral band emerged in the further intensified LLCC. The northern head of the comma-shaped cloud system was encircling the LLCC center. Line systems transversal and longitudinal to lower-level circulation were formed around MICA in the first sub-stage, and in the second sub-stage, respectively.LES and MICA constructed a kernel structure of Yancy on the early developing process. The MICA possessed a three dimensionally well organized structure for long lasting intense convection whose echo top attained 16km in height. The MICA and 500km scale LLCC appeared to mutually reinforce each other. Several aspects of the MPFs were summarized, which appear to correspond well to those numerically simulated mesoscale convection within developing tropical cyclone in Yamasaki (1983, 1986).

[学科分类] 大气科学