An Extreme-rain-producing Long-lived MCS during TiMREX: Possible Triggering and Maintenance Mechanisms

During Mei-Yu season in May-June, heavy precipitation frequently occurs in southern China and Taiwan. The combination of frontal lifting, southwesterly low-level-jet (LLJ) and mountain blocking in southwestern Taiwan provide a favorable setting for the development of convection and heavy precipitation. More often than not, most of the heavy rain falls on the foothill of the Central Mountain Range. However, during the Terrain-influenced Monsoon Rainfall Experiment (TiMREX), one long-duration extreme rain-producing mesoscale system developed offshore and dropped about a half meter of rain on the coastal cities. Inside this heavily precipitating system, new convection keeps developing offshore and feeding the large precipitation shield. We are able to describe the storm environment, vertical precipitation structure and possible microphysical processes of these convective cells. However, the fundamental cause for their persistent triggering and maintenance are still unknown. Our working hypothesis is that previous precipitation before the development of the long-duration system formed a “cold pool” over the island and adjacent ocean and the boundary between the “cold pool” and upstream moist air triggers new convection. This paper used detailed data from TiMREX to support the hypothesis. High-resolution storm environment data, 3D-storm structures, and dual Doppler wind field are analyzed.