Equatorial undercurrents associated with Indian Ocean Dipole events during contrasting summer monsoons

Abstract

Positive Indian Ocean Dipole (IOD) events generally tend to be accompanied by intensified summer monsoon flows and above normal precipitation over the sub-continent; although strong monsoons have not always coincided with positive IOD events. Numerical simulation experiments and supplementary data diagnostics are performed to understand the IOD sub-surface dynamics in relation to the monsoon strength. The model experiments when forced by IOD winds during strong monsoon periods generated a strong subsurface zonal pressure gradient along the equator and an eastward equatorial undercurrent (EUC) leading to supply of cold subsurface waters to the upwelling regions in the eastern equatorial Indian Ocean. However, the simulations when forced with IOD winds during weak monsoon periods were unable to set up the subsurface pressure gradients and the EUC, thus resulting in weak SST cooling in the east. These results raise the possibility that IOD-monsoon interactions during strong monsoon years might favor intensification of the IOD.