Abstract
A torrential rain episode (≧ 200 mm day^(-1)) was observed over coastal regions of southern Taiwan (south of 23.0°N) on 5 June 2008 under the influence of a meso-scale frontal cyclone (MFC) formed along the western flank of a Mei-yu frontal zone. Through the incorporation of additional observations over the ocean collected during Southwest Monsoon Experiment (SoWMEX)/Terrain-influenced Monsoon Rainfall Experiment (TiMREX), the location of a Mei-yu frontal boundary, defined by the wind shift, is better identified over the open ocean by the data assimilation of dropsonde observations. Meanwhile, the low-level cyclonic vorticity and horizontal convergence are increased along the Mei-yu frontal zone, and an increment maximum center of cyclonic vorticity locates over the north of South China Sea (SCS), where the MFC subsequently forms.For the development and maintenance of a MFC over the northern SCS, the additional data assimilation, using the combination of the dropsonde and the radar radial velocity, has significantly improved the prediction of an MFC with a best track over the open ocean. Therefore, the daily rainfall distribution and amount over southern Taiwan are reproduced and significantly improved, particularly using dropsonde observations combined with the radar radial velocity.
Highlights
Flash flooding and debris flow resulting from heavy rainfall have become the most important issue associated with natural disasters in Taiwan during the warm season (May-August)
The location of the Mei-yu frontal boundary is more consistent with the analysis of surface front by the Central Weather Bureau (CWB) of Taiwan as compared with the National Centers for Environmental Prediction (NCEP) global forecasting system (GFS) (Fig. 6b)
During 2008 Taiwan Mei-yu season, a torrential rain event (F 200 mm day-1) on 5 June occurred over coastal regions of southern Taiwan which is associated with an approaching meso-scale frontal cyclone (MFC) which developed over the north of the South China Sea (SCS) along the Mei-yu frontal zone during 4 - 5 June, 2008
Summary
Flash flooding and debris flow resulting from heavy rainfall have become the most important issue associated with natural disasters in Taiwan during the warm season (May-August). Based on weather and statistical rainfall analyses during the Taiwan Mei-yu season, the heavy rainfall is frequently produced in southwestern Taiwan (Chen et al 2007), while mesoscale convective systems (MCSs) embedded within the southwesterly monsoon flow and the Mei-yu front are primarily responsible for the production of the rainfall there (Chen and Chen 2003) under favorable large-scale conditions and the orographic effects (Chen et al 2005, 2007). Some weather analyses have revealed that rain-producing systems that cause heavy rainfall over southwestern Taiwan originate from the ocean near the southwest coast of Taiwan or form in the north of South China Sea (Chen et al 2005, 2010). To improve the prediction of associated torrential rainfall over southern Taiwan on 5 June is conducted
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