[A-CG43] Multi-scale ocean-atmosphere interaction in the tropics

[ACG43-P08] Role of ocean mixed layer and surface heat flux variations on the rapid decay of the 2019 positive Indian Ocean Dipole

*Takanori Horii¹, Iwao Ueki¹, Tengfei Xu², Shigeki Hosoda^1,3 (1.Japan Agency for Marine-Earth Science and Technology, 2.The First Institute of Oceanography, Ministry of Natural Resources, China, 3.Tohoku University & JAMSTEC Advanced Institute for Marine Ecosystem Change (WPI-AIMEC))

Keywords:Indian Ocean Dipole, Tropical Indian Ocean, Ocean mixed layer depth, Surface heat flux, Argo data

In 2019, a positive Indian Ocean Dipole (pIOD) event developed into one of the strongest in the past 30 years by October 2019 and rapidly decayed during November and December. This study investigates the mechanisms behind this rapid decay of the pIOD, focusing on variations in surface heat flux and mixed layer depth.
Argo observations in the tropical Indian Ocean were abundant in 2019, enabling high spatiotemporal analysis of ocean temperature, salinity, and mixed layer depth variations. Using the Argo data, we identified a shallow mixed layer distribution (~500 km off Sumatra and Java) from October to December 2019. During this period, the eastern Indian Ocean experienced positive net surface heat flux, driven by increased shortwave radiation and reduced latent heat cooling. Results suggest that the unusually shallow mixed layer enhanced the sensitivity of mixed layer temperature to surface heating, effectively warming the SST to decay the 2019 pIOD. These findings highlight the importance of mixed layer depth variability in modulating IOD decay processes.