Case Study of an Unusually Heavy Rain Event over Eastern Taiwan during the Mei-Yu Season

Abstract

A heavy rain event during the mei-yu season was observed over eastern Taiwan on 28 May 2001 under a potentially unstable environment with high CAPE and copious moisture. This event, with an unusually high daily rainfall maximum of 307 mm, was observed in the Ilan area over northeastern Taiwan. The retrogression of a mei-yu front over the nearby ocean collocated with a short-wave trough provided favorable large-scale conditions for the production of localized heavy rainfall. Latent heating was suggested to be responsible for the retrogression and the development of the mei-yu front over the nearby ocean to the east of Taiwan. In addition to the large-scale forcings, the local circulations and local topography modulated the rainfall distribution over the Ilan area. During the daytime hours, the strengthened onshore wind component due to the intensified mei-yu frontal circulation and orographic lifting provided enhanced rising motion over the windward slopes of the mountain to produce the significant rainfall. During the nighttime hours, although shallow subsidence was observed, moderate rainfall occurred over the mountainous region. This might be related to stronger orographic lift aloft as the strengthening of the easterly upslope wind component occurred. The heavy rainfall was observed over the coastal regions because the rain system over the nearby ocean moved inland. The rain system might be related to the development of a frontal cyclone along the western flank of the mei-yu front.