Dual-Doppler Radar Investigation of a Convective Rainband during the Impact of the Southwesterly Monsoonal Flow on the Circulation of Typhoon Morakot (2009)

　　　This study focuses on the characteristics and evolution of convections embedded within the principal band during the impact of the southwesterly monsoonal flow on the circulation of typhoon Morakot (2009) over Taiwan in use of dual-Doppler wind analysis. The southwesterly monsoonal flow impinged upon the typhoon circulation and resulted in the remarkable convergence which led to the initiation and development of convections in the rainband. 　　 The vertical kinematic characteristics of the rainband revealed that two types of downdrafts inner-edge downdrafts (IEDs) and low-level downdrafts (LLDs) were found. The IEDs coupled by the radially inward tilting convection was initiated by the precipitation drag. Dynamically, the existence of the perturbed high at 1.5 km altitude in the IEDs supported the finding. Furthermore, it is evident that the distribution of two perturbation highs in the vicinity of the rainband could lead to the SW flow deformation locally and fortify the mechanism of convergence as well as the merger of convective cells in the rainband. The noteworthy maximum vertical vorticity coupled with the horizontal wind maximum at middle levels of the rainband was also observed. The mesoscale mechanism (the interaction of SW flow and typhoon circulation) and convective scale mechanism (the merger of convective cores) would sustain the intensity of precipitable water in this unique principal band. The embedded convective cells consistently moved eastward, which might deliver a foreseeing factor for heavy rainfall over land.