Impact of Indian Ocean Dipole on the salinity budget in the equatorial Indian Ocean

摘要

Based on observations and ocean reanalysis, this study analyzes the variability of salinity and its related ocean dynamics in the equatorial Indian Ocean (IO). The results show significant interannual variability of salinity associated with the Indian Ocean Dipole (IOD) mode in the boreal fall. During the positive phase of IOD (pIOD), when anomalous easterly winds prevail, westward advection along the equator strengthens in summer, while the eastward advection associated with the Yoshida-Wyrtki Jet weakens in fall. Analysis of salinity budget indicates that salinity anomalies are mainly due to advection, of which zonal component is dominant. As zonal current anomalies are symmetric with respect to the equator, the equatorward large northern IO zonal salinity gradient is more important than the current anomalies in determining the asymmetric distribution of low-salinity advection. During the mature phase of pIOD, low-salinity water is advected westward, which in turn shoals the surface mixed layer, thereby providing a favorable condition for warmer sea-surface temperature in the western equatorial IO. During the decay phase of pIOD, low-salinity water is advected across the equator to the southwestern IO. When pIOD concurs along with El Nino, the strengthened off-equatorial anticyclonic circulations, which is associated with El Nino, advect low-salinity water poleward after the decay phase.