| dc.description.abstract | This study uses CWB QPESUMS radar, rain gauge, sounding, and ECMWF reanalysis data to investigate (Mesoscale Convective Systems) MCS events and analyze their synoptical environment characteristics in the Taiwan area from 2006 to 2020. The selected MCSs of five seasons, namely Spring, Mei-yu, Summer, Autumn and Winter, were analyzed.
The results show the Mei-yu season has the most MCS events (31.5%), the second most is spring (30.0%), and the least is the winter season (7.0%). In spring, MCS mainly associated with cold frontal system and located in northern Taiwan. The environment shows the southwesterly wind converged with winter monsoon in the lower level. The MCS events of the Mei-yu season are the most active with deepest convections. The environment shows there are upper-level divergence, deeper mid-level trough, and low-level jet. The MCS are located around retire Taiwan. The thermal condition is the most unstable to convection in Summer, the vertical wind shear is the weakest. Thus, Summer has lesser total number and weaker MCS events than Mei-yu season. The MCS events are mostly located in southwestern Taiwan and triggered by the southwesterly monsoon.
The instability starts to decrease after the winter monsoon onset. MCS mainly located in eastern and southeastern Taiwan in Autumn. Because of the dry and cold winter monsoon flow, the northerly wind component will decrease when MCS occurs in Autumn, causing the northeasterly wind turn to easterly or even southeasterly wind (especially after November). In addition, MCS events caused by the cold frontal system become more frequent in northern Taiwan after November. In winter, the environment is similar to November. However, because of the unfavorable convection condition, the frequency and convective strength are the lowest. | en_US |