Mesoscale Analysis on the Quasi-linear Convective System off the Southwest Coast of Taiwan during Southwesterly Flow Experiment (SoWFEX 2006)

Abstract Several remarkable convective systems associated with the Mei-yu frontal rainband were approaching the southern Taiwan area on 9-10 June 2006 during Southwesterly Flow Experiment (SoWFEX 2006). The plan position indicators of CWB Chiku Doppler weather radar illustrate that the intense echoes had developed into convective lines with bulge, which are often referred to quasi-linear convective systems (QLCS). The constant altitude plan position indicators of Chiku radar show that there existed a significant weak echo channel in rear of the apex, splitting intense echoes (> 40 dBZ) into two parts. The radial velocity reveals that a cyclonic shear was located on the northern part of the linear system between 2 to 5 km levels in altitude. One of the QLCS was observed by both Kenting and Chiku Doppler weather radars. Due to the good quality of collecting dataset, it is useful for Dual-Doppler wind synthesis. The synthesized wind fields delineate the existence of peak updraft in 8 m s-1 (Fig. 1)and affirm the shearing circulation with maximum vertical vorticity over 3×10-3 s-1 (Fig. 2) within the northern intense echo on the 3 km level. It also demonstrates an anticyclonic circulation embedded within the southern intense echo. The downdraft, which had a maximum of 5 m s-1, was collocated with the weak echo channel. It suggests that the formation of weak echo channel was related to the existence of the descending air.