Both the atmosphere-ocean interactions at the sea surface and the oceanic interior variabilities play important parts in regulating the surface mixed layer heat and salinity on sub-monthly to intraseasonal time scales in the central equatorial Indian Ocean. The surface heat flux and the oceanic turbulent heat flux at the base of the surface mixed layer are the two dominant terms that dictate the variation of the mixed layer heat content associated with MJOs. As for the salinity variation, the surface fresh water flux and horizontal advective flux are the two critical components, comparable in magnitude but opposite in sign. The former is largely associated with MJOs, whereas the latter exhibits noticeable bi-weekly frequencies. The turbulent salinity flux at the base of surface mixed layer is nontrivial and generally entrains saltier water to the mixed layer; therefore, resulting in a gradual increase of mixed layer salinity over the fall to early winter season.
The central equatorial Indian Ocean is an interesting area where distinct water masses meet in both zonal and meridional directions, e.g. by the semiannual eastward zonal jet centered at the equator during monsoon transitional seasons and by oceanic equatorial waves, which complicates the oceanic surface mixed layer budgets. The quasi-permanent oceanic barrier layer that is suggested to retard the cooling of SST during surface wind events in fall leads to further complexities of the upper ocean dynamics at the central equatorial Indian Ocean.