Interannual Rainfall Variability over Northwestern Jawa and its Relation to the Indian Ocean Dipole and El Nino-Southern Oscillation Events

Interannual rainfall variability over northwestern Jawa, Indonesia and its relation to the Indian Ocean Dipole (IOD) and El Nino-Southern Oscillation (ENSO) events were investigated using daily rainfall data for 1973-2008. IOD events clearly influence interannual rainfall variation in the dry season (May-October) in northwestern Jawa. Drought conditions during the dry season occur in conjunction with simultaneous development of positive IOD and El Nino events, whereas wet conditions tend to appear in negative IOD (with or without La Nina) rather than single La Nina events. During positive (negative) IOD years, cooler (warmer) sea surface temperature (SST) surrounds the maritime continent and large-scale divergence (convergence) and lower (higher) atmospheric water vapor content are observed. These conditions tend to suppress (induce) rainfall in northwestern Jawa. On the other hand, interannual rainfall variation in the rainy season (November-April) is not closely related to ENSO/IOD, but rainfall tends to be abundant in neutral (non-ENSO/IOD) years. This may be influenced by Northern Hemisphere winter monsoon strength and/or northerly (cold) surges. Furthermore, decreasing trends are detected for rainfall amounts and number of rainy days in the rainy season.