Interactions among ENSO, the Monsoon, and Diurnal Cycle in Rainfall Variability over Java, Indonesia

Using a high resolution regional climate. model the Abdus Salam International Centre for Theoretical Physics Regional Climate Model version 3 (RegCM3)-and station and satellite observations the authors have studied the spatial heterogeneity of climate v.-inability over Java Island Indonesia Besides the well known anomalous dry conditions that characterize the dry and transition seasons during an El Nino year analysis of regional model output reveals a wet mountainous south versus dry northern plains in precipitation anomalies associated with El Nino over Java during the peak rainy season Modeling experiments indicate that this mountains/plains contrast is caused by, the interaction of the El Nino-induced monsoonal wind anomalies and the island/mountain induced local diurnal cycle of winds and precipitation During the wet season of El Nino years anomalous southeasterly winds over the Indonesian region oppose the climatological northwesterly monsoon thus reducing the strength of the monsoon winds over Java This weakening is found to amplify the local diurnal cycle of land-se's breezes and mountain-valley winds producing more rainfall over the mountains which are located closer to the southern coast than to the northern coast Therefore the variability of the diurnal cycle associated with this local spatial asymmetry of topography is the underlying cause for the heterogeneous pattern of wet south/dry north rainfall anomalies during El Nino sears It is further shown that the mean southeasterly wind anomalies during December-February of El Nino years result from more frequent occurrence of a quiescent monsoon weather type during who h the strengthened sea breeze and valley breeze convergence leads to above normal rainfall over the mountains