Abstract
Simultaneous observations with a UHF-band boundary layer radar (hereafter referred as BLR), GPS rawinsondes and a tipping-bucket-type rain gauge were conducted at Kototabang (0.20°S, 100.32°E, 865 m MSL), which is located on the mountainous region near Bukittinggi, West Sumatera Province, during 27 September-7 October 1998 (rainy season). Low-level (1-3 km) westerly wind stronger than 10 m/s was observed, and precipitation tended to occur when the low-level westerly wind became weak (2-5 October). Similar relationship was observed for two months (1 September-31 October 1998) during which only BLR and surface meteorological instruments were operated at Kototabang. NCEP/NCAR objective analysis, and GMS TBB data showed that the low-level (850 hPa) wind field, and cloud distribution, were both completely different between the Indonesian Archipelago (east of Kototabang) and the eastern Indian Ocean—including the Bay of Bengal (west of Kototabang)—uring the analysis period.
Two large-scale cloud disturbances existed along the equator in the western side (80°-100°E), but precipitation at Kototabang did not correspond to these cloud disturbances. The implication is that effects of the mountain range of Sumatera blocked the large-scale cloud disturbances over the Indian Ocean. The precipitation by local-scale cloud systems prevailed at Kototabang. The convergences of local circulations, which are generally dominant under weak background winds, are considered as the major cause of local-scale cloud systems.
