Fig. 6: Schematic diagrams illustrating the formation mechanism of the extreme IOD spatial asymmetry.

a JJA SSTAs and subsurface temperature anomalies during EXpIOD events, which nearly constitute a mirror image relative to those of b EXnIOD events. The blue three-dimensional coloured arrows represent nonlinear cold advections in cooperation with the anomalous equatorial and coastal vertical motions at the bottom of the mixed layer. Nonlinear vertical advections and asymmetric latent heat flux jointly reshape the existed SST pattern and further lead to the evident pattern asymmetry between c EXpIOD and d EXnIOD in SON.