Surface Mixed Layer Salinity Budget in the Tropical Indian Ocean

The oceanic surface mixed layer salinity budget is evaluated during Madden–Julian Oscillation (MJO) events in the central equatorial Indian Ocean. As part of the DYNAMO field campaign (September 2011 – January 2012), three MJO events were recorded at two mooring sites (0S 79E and 1.5S 79E). The surface mixed layer freshens during two strong MJO wet phases, but salinity increases, mostly due to advective flux divergence, at all other times. The residual flux, presumably dominated by the turbulent salinity flux, is not negligible during MJO wet phases.

The surface mixed layer in the central equatorial Indian Ocean is generally shallow (20 m), often due to the shallow halocline, instead of thermocline. Salinity stratification dominates in the upper ocean, leading to persistent barrier layer. DYNAMO observations demonstrate that an accurate surface mixed layer parameterization that includes upper ocean salinity and temperature processes is needed to improve model predictions of MJO initiation and evolution, as well as the oceanic responses to MJO events.