3C.6
Characteristics on the mesoscale convective systems organized in the process of typhoon formation over the western north Pacific
PAPER WITHDRAWN
Kazumasa Mori, MRI, Tsukuba, Ibaraki, Japan
In the western north Pacific, the Japan Meteorologycal Agency(JMA) research vessel(R/V) Keifu Maru made observational cruises with radar observations to understand the characteristics of mesoscale convective systems(MCSs) organized in the process of typhoon formation every summer in '90. Using the radar data, three cases were presented as observational documentation of MCSs organized in the central area of forming typhoons. In the firat case of typhoon Yancy(T9313) in the early developing stage, a long lasting, intense and three dimensionally well organized MCS associated with low level direct inflow with wind speed over 25 m/s was formed. After the formation of the MCS, low level cyclonic circulation (LLCC) appeared to be intensified on mesoscale. In the second case of typhoon Rex(T9804) in the forming stage, a pre-existing MCS once decayed and next new MCS formed within a LLCC. The latter MCS developed to a kernel structure of the forming Rex. In the third case of low-latitude low pressure area in Novemver 1999, which was a pre-disturbance of a tropical depression (TD), eastward moving MCS and east-northeastward moving MCS merged each other around a low level confluent line between westerly wind and west-southwesterly wind. Through the MCS meregr, mesoscale intense convection was organized.
These cases of MCSs within forming typhoons were discussed referring conceptual models of typhoon formation based on case studies with satellite images(Grey,1993;Zehr, 1992). The MCS in typhoon Yancy appeared to be a mesoscale precipitation entity of convective surge associated with low level 'wind surge(Grey,1993)'. The succsesive formation of two MCSs within typhoon Rex might be an example of 'two succsesive deep convective surges(Zehr,1992). The third case of the MCS meregr suggests that MCS merger might be a favorable process to organize intense and long lasting MCS in the early stage of typhoon formation. Synthesizing these observed three cases of MCSs from pre-TD to early developing stage of typhoons, a conceptual model of typhoon formation was presented, in which mesoscale convective phenomena such as MCS merger, successive formation of MCS within large scale LLCC or convective surge associated with wind surge are crucial for typhoon formation.
Session 3C, Tropical Cyclogenesis III
Monday, 3 May 2004, 1:30 PM-3:15 PM, Napoleon II Room
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