Impact of intraseasonal salinity variations on sea surface temperature in the eastern equatorial Indian Ocean

A systematic salinity variation in the upper ocean may have an impact on air-sea interactions through a change in ocean stratification and hence on the oceanic response to atmospheric forcing. In this study, we evaluate the possible role of salinity variation in the oceanic response to intraseasonal atmospheric forcing, by investigating the ocean temperature and salinity variation in the eastern Indian Ocean. We primarily used data from three moored buoys located in an area with a large salinity gradient in the eastern equatorial Indian Ocean. Observed upper-layer salinity variation shows significant spectral peaks at intraseasonal time scales. Analysis indicates that surface zonal currents mainly produce the intraseasonal salinity variation through zonal advection with these currents induced by the Madden-Julian Oscillation (MJO). Composite analyses focusing on 35 significant MJO events during 2002-2012 confirmed that intraseasonal atmospheric forcing resulted in variations of net surface heat flux, mixed layer temperature and salinity, and mixed layer depth. We also found that a large salinity change could increase the amplitude of mixed layer temperature variation by changing the mixed layer depth. A possible process by which intraseasonal salinity variation could affect sea surface temperature is discussed.