dc.description.abstract | The southwestern Taiwan heavy rainfall event, on 12 august 2014, with a maximum rainfall of 345.5mm, and moreover, the rainfall are distributed over lowland and coast area. In summer, usual rainfall are produced on windward side of southwestern Taiwan, come from southwesterly monsoon and convective systems follow monsoon flow. In order to identify the synoptic environments associated with the 12 August 2014 heavy rainfall event and its mechanism, this study will perform observational analyses of the European Centre for Medium-Range Weather Forecasts (ECMWF) data, satellite imagery, radar reflectivity, rainfall data, and Weather Research and Forecasting (WRF) Model. The simulation results from the WRF model will compare with observation data to identify the mechanisms resulted to this localized heavy rainfall.
Through the analysis of ECMWF/ERA-Interim data shows that there were more water vapor flux in 2014 average than ten years (2005~2014) average synoptic environments, and there is a low pressure over southern of Japan on 850hPa, and monsoon trough extended from southern China to east of Taiwan, as a result, raising motion area over Taiwan conduce clouds developed. On 12 august 2014, there is low-level water vapor convergence on 950hPa, and cyclone circulation over northern South China Sea and Bashi Channel, it’s also promote clouds developed. We found that the mainly heavy rainfall areas in 12 August 2014 are in the lowland area and the stronger convergence induced by southwesterly monsoon and down-slop wind and southeastern wind which the monsoon flow deflected by orographic effect, and the convective system follow monsoon flow moved in lowland area from southwestern Taiwan offshore region.
In the simulation result, it can also see the same heavy rainfall mechanisms which the convergence was produced by the convergence between the prevailing wind and the down-slop wind, and the deflection wind. But the offshore convective systems did not move in to southwestern Taiwan, the rainfall in early day did not simulate well. Through by 27km grid WRF simulation result, we can see on 700hPa lacking east wind resulted in less convective systems had been enhanced.
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