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Structure and Evolution of Convection Within Typhoon Yancy (T9313) In Journal of the Meteorological Society of Japan, Vol. 77, No. 2,, pp. 459-482, 1999 459 Structure and Evolution of Convection within Typhoon Yancy (T9313) in the Early Developing Stage Observed by the Keifu Maru Radar By Kazumasa Mori MeteorologicalResearch Institute, Tsukuba, Japan Syuji Ishigaki Nagasaki Marine Observatory, Nagasaki, Japan Takao Maehira, Masakatsu Ohyal Climate and Marine Department, Japan MeteorologicalAgency, Chiyoda-ku, Tokyo, Japan and Hitoshi Takeuchi Tokyo District MeteorologicalObservatory, Chiyoda-ku, Tokyo, Japan (Manuscript received80 March 1998, in revised form 8 January 1999) Abstract 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 80 km 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 (CETwinds) 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-levelcyclonic circulation (LLCC) of 1500 km 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 (100-500 km) 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 (400 km) 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 500 km 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 500 km 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-levelcirculation were formed around MICA in the first sub-stage, and in the second sub-stage, respectively. Corresponding author: Kazumasa Mon. Present affilia- 1 Present affiliation: Fukuoka District Meteorological Ob- tion: Climate and Marine Department, Japan Meteoro- servatory, Oohori, Chuo-ku, Fukuoka, Japan. logical Agency, Chiyoda-ku, Tokyo, Japan. 1999, Meteorological Society of Japan 460 Journal of the Meteorological Society of Japan Vol. 77, No. 2 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 16 km in height. The MICA and 500 km 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). 1. Introduction able common cloud features in the early developing Understanding a formation and early develop- stage of TCs. ing process and mechanism of a tropical cyclone Concerning the central mesoscale features of for- mation and early developing process of TCs, virtu- (TC) has been one of the fundamental problems in tropical meteorology. So far, several case stud- ally no radar observation has been done. Therefore, ies have been made on these issues mainly using it is not clear how the convection is organized un- special observational experiment opportunities con- der the well known cloud feature of CDO. Mesoscale ducted over the tropical ocean. Yanai (1961) an- events analyzed by Zipser and Gautier (1978) first alyzed a typhoon synoptic scale formation process appear to be radar observed central mesoscalefea- transformed from an easterly wave disturbance with tures of TC in the early developingstage. However, cold core structure using special dense upper-air ob- because of the shortage of period and time inter- servation data over the tropical Pacific Ocean. Us- vals of the aircraft radar observation, the evolution ing the Australian Monsoon Experiment (AMEX) process and three dimensional structure were not data, Davidson et al. (1990) analyzed synoptic to described in detail. This is contrastive to mesoscale cyclonic scale changes during the formation of TCs, features within mature TCs, such as eyewall clouds and indicated low level spinup. and spiral bands, which have been investigated ex- As for mesoscale aspects of forming and early de- tensively using airborne Doppler radar (e.g., Barns veloping TCs, rare observations have been done. et al., 1983; Marks and Houze, 1987) and ground Zipserand Gautier (1978)analyzed mesoscaleevents based dual Doppler radar (e.g., Ishiraha et al., 1986; within a tropical depressionwhich intensified around Tabata et al., 1992; Shimazu, 1997). the Global Atmospheric Research Program's At- Since a concept of conditional instability of the lantic Tropical Experiment (GATE) area, and noted second kind (CISK), which is an instability of the that a deep convection mesoscale organization pre- atmosphere in which a large-scale disturbance de- ceded mesoscale cyclogenesis. Mesoscale structure velops through interaction with cumulus convec- of a wide rainband in a developing typhoon was tion and large-scale circulation, was presented by investigated using aircraft data in the Equatorial Ooyama (1964) and Charney and Eliassen (1964), MesoscaleExperiment (EMEX) (Ryan et al., 1992). a number of numerical simulations of TC develop- Recently, the Tropical Cyclone Motion field exper- ment have been done using a parameterization of iment (TCM-93) was conducted over the western convection based on the theoretical concept (e.g., tropical Pacific, and a mesoscale convective system Yamasaki, 1968; Ooyama, 1969). Yamasaki (1983) investigated the interaction between cumulus con- (MCS)-embedded in an intensifying typhoon - was investigated using an aircraft-equipped Omega vection and large scale motion during the devel- dropsonde system (Harr and Elsberry, 1996). opment of TC, using a two dimensional numerical In addition to these case studies - which were model in which convection was treated explicitly, fruits of epoch making field experiments-contin- and categorized the simulated mesoscaleconvection uous efforts to incorporate newly obtained meteoro- in the developing TC three types depending on the logical satellite data into the analysis of TC genesis role of surface friction. Further, Yamasaki (1986) and early development have been made since the developeda three-dimensional TC model with a new 1960's. For example, Hawkins and Rubsam (1968) parameterization of convection based on the results described a formation of hurricane Hilda in detail of Yamasaki (1983) and performed a numerical ex- combining satellite photographic data with aircraft periment, in which the simulated mesoscalefeatures and conventional data. Recently, Liu et al. (1994) were discussed using the category of convection, investigated the structure and atmospheric water and compared them with several observational facts. balance of typhoon Nina through its life cycle in- Yamasaki (1989) studied tropical cycloneformation cluding formation and developing stages using data in the intertropical convergence zone (ITCZ). Re- from the Special Sensor Microwave/Imager (SSM/I) cently, Nasuno and Yamasaki (1997) discussed long- on the Defense Meteorological Satellite Program lived mesoscaleconvection simulated in the basically the same Yamasaki model (1983) with extended ar- (DMSP) satellite. Further, a general model of TC development cloud patterns was presented on the eas. basis of the morphology of numerous TCs cloud fea- Continuing the above described progress of tures (Dvorak, 1975), in which the central dense TC numerical experiment development, Yamasaki overcast (CDO) was noted as one of the remark- (1988) remarked that more interaction between ob- April 1999 K. Mori, S. Ishigaki, T. Maehira and et al. 461 Fig. 1. Track and central pressure of Yancy. Thick line is a best track of Yancy, small marks show locations of Yancy at 00 UTC, and numerals near the marks are date and central pressures. On 30 and 31 August, locations of Yancy are marked every six hours. Track of the center of lower-level cyclonic circulation derived from CETwinds during 18 UTC 30 August to 12 UTC 31 August is shown by dotted line in which locations of the center every three hours are marked by larger dots. K' indicates Keifu Maru's location and shaded square shows radar observation area. 'TD', 'TS', ' etc. show intensity of Yancy. servational and modelingstudies is desirable for bet- proached within 80 km north of the ship during the ter understanding of the formation and early de- radar observation. Convection
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