| Summary: | 碩士 === 國立臺灣師範大學 === 地理學系 === 106 === From the perspective of climate classification, this study classifies the spatial distribution of rainfall in the Meiyu front during the rainy season in Taiwan. The data are based on the 1km resolution daily rainfall grid database from 1960-2016 and the daily rainfall database from the standardized Z-score stations all over Taiwan.
First, the daily rainfall totals of the Meiyu days and Meiyu events are defined to select the rainy days that meet the amounts. Empirical orthogonal functions and rotating empirical orthogonal functions are then used to classify these Meiyu days into six rainfall spatial patterns, including the coastal areas in the southwest, the sections in the north, the western coastal areas, the mountainous areas in Central Mountain Range, the eastern coastal areas and the northwestern regions.
The average daily rainfall distributions of the six spatial distribution patterns are averaged to obtain the average rainfall distribution of the six spatial distribution patterns. Based on the analysis of the circulation data and the rainfall distribution of spatial patterns using the European Reanalysis-Interim (ERA-Interim) of European centre for Medium-Range Weather Forecasts (ECMWF), the large-scale circulation anomaly fields coupled with the six spatial distributions are analyzed, including the pressure anomaly field, vertical velocity anomaly field, and the development characteristics of the streamlined anomalous field. These analyses are utilized to detect the large-scale circulation state of the six rainfall spatial patterns.
The long-term trend of identified spatial distribution patterns are also analyzed to detect their possible frequency and intensity changes based on the bootstrap method. For the frequency changes, it is found that the spatial patterns 3, 4 and 5, mainly located in the western coastal areas, the Central Mountains Range and eastern coastal areas individually, showed a -1.94/100-yr, -6.4/100-yr and -2.57/100-yr reduction, respectively. As for the intensity changes, the spatial pattern 4 (i.e. Central Mountain Range) has a significant 29.42mm/100-yr rising trend, and all (i.e. the unsorted) spatial distribution patterns Meiyu events have an 11.71mm/100-yr rising trend.
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