Impact of intraseasonal salinity variations on sea surface temperature in the eastern equatorial Indian Ocean
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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.
KeywordsSurface salinity Ocean stratification Eastern Indian Ocean Mixed layer temperature Madden–Julian oscillation RAMA buoy
We thank all of the members of the R/V Mirai and the data processing team of the Triangle Trans-Ocean Buoy Network (TRITON) buoy cruise operations for their data management. We also thank the US National Oceanic and Atmospheric Administration (NOAA)/Pacific Marine Environmental Laboratory (PMEL) and National Institute of Oceanography (NIO) for providing RAMA buoy data, and the NOAA-Cooperative Institute for Research in Environmental Sciences (CIRES) Earth System Research Laboratory (ESRL)/Physical Sciences Division (PSD) for providing SST data and reanalysis flux products. The TropFlux data were produced through a collaboration between Laboratoire d’Océanographie: Expérimentation et Approches Numériques (LOCEAN) from Institut Pierre Simon Laplace (IPSL, Paris, France) and the National Institute of Oceanography/CSIR (NIO, Goa, India), and it was supported by the Institut de Recherche pour le Développement (IRD, France). We thank two anonymous reviewers for valuable comments and suggestions.
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