Abstract
Abstract
Rainfall over the Indonesian Maritime Continent (IMC) is strongly modulated by the El Niño-Southern Oscillation (ENSO), yet most previous studies have neither resolved ENSO intensity in detail nor examined rainfall jointly with atmospheric instability and low-level moisture. This study characterizes the spatial patterns of rainfall, Convective Available Potential Energy (CAPE), and 925 hPa relative humidity (RH925) anomalies across six ENSO intensity classes (weak, moderate, and strong El Niño and La Niña) over the IMC, using ERA5 reanalysis data for 1995–2025. ENSO phases were classified using the Oceanic Niño Index (ONI). The significance of the composite anomalies was assessed with a one-sample t-test and non-parametric bootstrap resampling (95% confidence interval, 1000 iterations), and the consistency between the two approaches was evaluated. Rainfall and RH925 responded uniformly but with opposite sign to the two ENSO phases, showing deficits during El Niño and surpluses during La Niña, with magnitudes that increased from weak to strong events. In contrast, CAPE anomalies did not vary monotonically with intensity but formed a west–east dipole that sharpened during moderate and strong phases. The two significance tests yielded highly consistent spatial patterns for all variables and phases. During strong events, rainfall and RH925 displayed an asymmetric response: the area of significant anomalies expanded under El Niño but contracted under La Niña, whereas the significant CAPE anomalies were spatially redistributed.