The influence of El Niño-Southern Oscillation (ENSO) on the characteristics of tropical cyclones in Indonesia waters

Indonesia, bordered by the Indian and Pacific Oceans, is influenced by tropical cyclone (TC) activity and phenomena such as the El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD). This study examines TC variations across four Indonesian regions, focusing on ENSO events when the IOD is neutral. Over the past 50 years (1973–2022), 2,885 tropical cyclones (TCs) have passed through Indonesian waters, with the most active area being Region 2. During El Niño, TC occurrences across Indonesia increase, while La Niña sees fewer TCs overall but with regional variations. Region 2 experiences a 12.5 % monthly decrease in TCs during La Niña due to less favourable environmental factors like vertical wind shear (VWS) and vorticity. Conversely, Regions 3 and 4 show increases of 38.1 % and 45.7 %, respectively, attributed to supportive conditions such as sea surface temperature and humidity. Accumulated Cyclone Energy (ACE) analysis reveals significant changes, with increases of 65.4 % in region 1 and 12.4 % in region 2 during El Niño, while region 2 decreases by 35.3 % during La Niña. Kernel Density Estimation (KDE) highlights seasonal and ENSO-driven spatial shifts, with density centres generally moving eastward during La Niña, except for region 2, which shifts westward. The largest shift, 632.1 km, occurred in region 4 during La Niña, moving TC formations from near West Nusa Tenggara to the Timor Sea. Analysis of Significant Wave Height (SWH) during ENSO periods for each tropical cyclone event in different regions shows that shifts in density centers during El Niño and La Niña also influence SWH variability in Indonesian waters. These findings underscore the impact of ENSO on TC activity in Indonesian waters, providing valuable insights for improving preparedness and marine safety.