Roles of Equatorial Ocean Currents in Sustaining the Indian Ocean Dipole Peak

In this study, on the basis of the results of the European Centre for Medium-Range Weather Forecasts Ocean Reanalysis System 4, the response of equatorial ocean currents and their roles during the peak phase of the Indian Ocean Dipole (IOD) are comprehensively explored. During the IOD peak season, a series of ocean responses emerge. First, significant meridional divergence in the surface layer and convergence in the subsurface layer are found in the equatorial region. The equatorial easterly winds and off-equatorial wind curl anomalies are found to be responsible for the divergence at 55°–80°E and the convergence at 70°–90°E. Second, the meridional divergence and convergence are found to favor a weakened Wyrtki jet (WJ) in the surface layer and an enhanced Equatorial Undercurrent (EUC) in the subsurface layer, respectively. Therefore, these ocean responses provide ocean positive feedback that sustains the IOD peak as the weakened WJ and enhanced EUC help maintain the zonal temperature gradient. Additionally, heat budget analyses indicate that the weakened WJ favors sea surface temperature anomaly warming in the western Indian Ocean, whereas the enhanced EUC maintains the sea surface temperature anomaly cooling in the eastern Indian Ocean.