Influences of Indian Ocean Dipole and El Niño–Southern Oscillation on Thunderstorm Events in Indonesia

Understanding the influence of the El Niño–Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) on thunderstorm variability is critical for improving the accuracy of thunderstorm predictions in Indonesia. This study examines thunderstorm variability using nine combination modes of ENSO (La Niña/El Niño) and IOD (positive/negative) derived from the Southern Oscillation Index (SOI) and Dipole Mode Index (DMI) between 1993 and 2022. This study used monthly gridded flash rate density (FRD) data from 1995 to 2015, and thunderstorm days derived from 3-hourly surface weather reports from the 65 Indonesian Agency for Meteorology, Climatology and Geophysics (BMKG) stations from 1993 to 2022. Previous studies generally show that El Niño tends to increase thunderstorm activity in Indonesia, while La Niña tends to reduce it; however, the precise impacts of their interactions with the Indian Ocean Dipole (IOD) remain poorly understood. This study provides new insights into how combined ENSO–IOD phases drive distinct and regionally varied thunderstorm patterns across the Indonesian archipelago. We demonstrate that La Niña significantly reduces thunderstorm activity when specifically paired with a positive IOD phase, due to weakened moisture transport, cooler surface temperatures, reduced Convective Availability Potential Energy (CAPE) and diminished moisture convergence. Conversely, La Niña combined with neutral or negative IOD phases enhances thunderstorm activity in central and eastern Indonesia through increased moisture availability, surface heating and atmospheric instability. El Niño typically intensifies thunderstorms in western Indonesia, especially under neutral or negative IOD conditions, driven by increased surface air temperatures and enhanced CAPE; however, El Niño combined with a positive IOD notably suppresses convection nationwide due to decreased surface air temperature, moisture divergence and reduced CAPE.