Multi-Scale Climate Processes and Rainfall Variability in Sumatra, Peninsula Malaysia and Singapore Associated with ENSO in Boreal Fall and Winter (#1043)
The impact of ENSO (El Niño-Southern Oscillation) on the rainfall variability over Sumatra, Peninsula Malaysia and Singapore has been investigated by using station, satellite and reanalysis data, from the perspective of multi-scale processes of diurnal cycle, daily weather types, monsoon and ENSO. The rainfall variability is not spatially coherent in both SON and DJF in this region. In SON, there are more weather type 2 (WT2) and fewer WT3 in El Nino years, thus the seasonal rainfall anomaly pattern in SON is similar to that of WT2, with wet anomalies in western Peninsula Malaysia and northern Sumatra, and dry anomalies in southern Sumatra. In DJF of El Nino years, there is an area of wet anomalies in the southern tip of Malay Peninsula, including Singapore, and in central Sumatra, and slightly dry anomalies in central Malay Peninsula and northern Sumatra. There are more days of WT4 and fewer days of WT3 and WT5 in the DJF of El Nino years. In the early northeast monsoon season (Dec-Jan) when the ITCZ is still north of or near the equator, the El Nino-enhanced easterly wind anomaly on 850 hPa favors more frequent WT4 with more zonally oriented east-northeasterly winds, which propagate rainfall from the area of above normal SST in the southern South China Sea toward Singapore and adjacent seas to produce above normal rainfall. In February, however, more frequent WT4 will not enhance rainfall in the vicinity of Singaporean because the ITCZ has already moved to the southern hemisphere, and upstream area in the South China Sea is quite dry. This explains why the Singapore station observation shows dry anomalies in SON, wet anomalies in December and January, and dry anomalies again in February in El Niño years.