Spring Diurnal Precipitation over Luzon Island: Interannual Variability and Underlying Mechanisms

This study investigates how El Niño–Southern Oscillation (ENSO) modulates the diurnal cycle of springtime precipitation over Luzon Island, where complex terrain and strong land–sea interactions shape precipitation variability. The analysis focuses on three key precipitation indices, including mean precipitation (MP), diurnal precipitation variation (DPV), and rainy-day frequency (RD), to characterize springtime precipitation features and their interannual variability. Results show that all three indices exhibit a dominant 3–7-yr periodicity associated with ENSO and significant correlations with Niño-4 sea surface temperature anomalies, with stronger correlations for MP and DPV. Composite analyses indicate that ENSO modulates both the large-scale circulation and local thermodynamic environments governing diurnal convection over Luzon. During El Niño events, anomalous western North Pacific anticyclones over the South China Sea enhance subsidence, strengthen low-level westerlies, reduce moisture transport, and create drier and more stable atmospheric conditions, thereby suppressing convection and decreasing MP, DPV, and RD. In contrast, La Niña events produce the opposite conditions, favoring moisture convergence, upslope lifting, and more active afternoon convection. Consequently, ENSO modulates not only the precipitation amount but also its diurnal structure and event frequency over Luzon. These findings improve understanding of ENSO’s downstream impacts and provide insights relevant to seasonal precipitation variability and its predictive interpretation over tropical island regions.