2008 Volume 86 Issue 5 Pages 593-611
Pentad rainfall data from 46 stations in West Sumatera Province, Indonesia in 1992 reveal temporal and spatial variations of rainfall in coastal and inland regions. Distinct contrasts in rainfall amounts and variations are evident between the coastal and inland mountainous regions. Locality index is defined by pentad rainfall time series in coastal and inland regions to classify characteristic rainfall distribution patterns into four types: coastal-, inland-, active-, and inactive-type. In 1992 the coastal- or active-type rainfall patterns tend to appear throughout the year, whereas the inland-type rainfall pattern tends to appear during the Southern Hemisphere summer. The inactive-type tends to appear during the Southern Hemisphere winter.
Correlation and composite analyses suggest that lower tropospheric zonal wind variations over central western Sumatera tend to intensify the contrast between coastal and inland rainfall distribution. The correlation coefficient between locality index and zonal wind of 850 hPa NCEP/NCAR reanalysis is 0.77 (99% confidence level) for characteristic rainfall distribution patterns during 1992-1993. This implies that rainfall in the windward side of steep mountain is relatively greater than that of leeward side with increasing wind speed. The occurrence of coastal-type pattern is relatively well related with lower tropospheric westerly wind. Furthermore, although the number is limited, diurnal variations of convective activity are clear when active-type rainfall appears.