Relation Between Interannual Variability of Regional-scale Indonesian Precipitation and Large-scale Climate Modes in the Last Half Century

Regional-scale precipitation responses over Indonesia to major climate modes in the tropical Indo–Pacific Oceans, i.e., canonical El Niño, El Niño Modoki, and Indian Ocean Dipole (IOD), are investigated using a terrestrial precipitation dataset, Asian Precipitation-Highly Resolved Observational Data Integration Towards Evaluation (APHRODITE). The spatial resolution of the precipitation data is 0.5° x 0.5°, much higher than the precipitation datasets used in previous studies, allowing us to clarify spatial patterns of precipitation responses including their seasonal evolution in greater detail. Also the mechanism of spatial-seasonal development of precipitation responses is investigated by analyzing moisture flux convergence based on the JRA55 reanalysis data. Canonical El Niño strongly reduces precipitation in the central to eastern Indonesia from July to November and northern Indonesia from January to April, consistent with anomalous moisture flux convergence. It is found that the corresponding moisture flux convergence anomalies occur around the edge of the SPCZ (ITCZ), i.e., zero climatological convergence, in the period when seasonal migration of those edges comes to 10–15°S (10–15°N) from April–November (December–May) in the tropical west Pacific Ocean. This means that the seasonal migration of convergence zones is modulated by canonical El Niño strongly in the convergence zone edges, and this modulation explains regional and seasonal developments of precipitation responses. Similar precipitation responses are also found for El Niño Modoki associated with the anomalous moisture flux convergence with slightly different spatio-temporal patterns from those for canonical El Niño. IOD reduces precipitation in western Indonesia from July to November accompanied by moisture flux convergence anomalies in the Indian Ocean, and the seasonal dependency of precipitation anomalies is likely to be caused by the seasonal march of SST anomalies in the eastern pole of the IOD.