This study performed high-resolution numerical simulation on a convective line that occurred roughly 1030 km offshore of southeastern Taiwan overnight of 1415 May 1998. Three experiments at successively higher resolution (10, 2, and 0.5 km) but smaller domain were carried out, and the narrow line is eventually reproduced. It is found that shallow (offshore) return flow along the coast appeared since daytime due to topographic blocking on the weak prevailing (onshore) south-southeasterly wind, producing convergence at their interface near shore. During the night, mountain breeze further strengthened the offshore flow and convergence, and the line initiated. Once developed, downdrafts and outflow boundaries from old clouds triggered new clouds, and this was more active along the (eastern) boundaries against the undisturbed environmental flow. Thus, repeated new cloud formation took place throughout the night and into the next morning.
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