2012 Volume 90 Issue 5 Pages 617-628
This study investigates the mesoscale interaction of typhoon circulation and southwesterly flow during the passage of Typhoon Morakot (2009) over Taiwan using radar observations. Single Doppler radar analysis characterized typhoon features with remarkably distant rainbands, and identified the strong southwesterly monsoonal flow with a maximum speed of more than 45 m s-1 in the southern flank of distant rainbands. Dual-Doppler synthesized winds elucidated a confluent mechanism on the northern side of the rainbands with a maximum convergence over 1.5 × 10-3 s-1. Velocity azimuth display (VAD) winds showed the intensification of southwesterly flow at low levels. The southwesterly monsoonal flow initiated about 6 hrs before typhoon landfall, and then became prominently involved with typhoon circulation. Also, the radial component with respect to the typhoon center was enhanced and became comparable with the tangential one (～30 m s-1) about 7.5 hrs after landfall. The variation in intensity of radial components can be regarded as a unique precursor for the extension of influence of the southwesterly monsoonal flow onto the typhoon circulation. Furthermore, the strong convergence showed that the interaction between the southwesterly flow and typhoon circulation might contribute to the development of rainbands, as well as the intensification of the inward radial flow embedded within typhoon.
