A sea surface salinity dipole mode in the tropical Indian Ocean
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Based on the 10 years sea surface salinity (SSS) data from Argo, we identified a salinity dipole mode in the tropical Indian Ocean, termed S-IOD: a pattern of interannual SSS variability with anomalously low-salinity in the central equatorial and high-salinity in the southeastern tropical Indian Ocean. The S-IOD matures in November–December, lagging the Indian Ocean dipole (IOD) mode derived from sea surface temperature (SST) by 2 months. For the period of observations, the S-IOD persists longer than the IOD, until the following September–October. Oscillations of the two S-IOD poles are governed by different processes. Ocean advection associated with equatorial current variability dominates the SSS anomalies of the northern pole, while surface freshwater flux variability plays a key role in the SSS anomalies of the southern pole, where anomalous precipitation is sustained by preformed sea surface temperature anomalies. The S-IOD concurs with the strong IOD, reflecting an ocean–atmosphere coupling through the SST-precipitation-SSS feedback.
KeywordsS-IOD SST-precipitation-SSS feedback Tropical Indian Ocean Argo
We acknowledge the International Argo Program for providing Argo data (http://www.argo.ucsd.edu). The GPCP precipitation was obtained from the NASA/GSFC (http://precip.gsfc.nasa.gov). The OAFlux evaporation was provided by WHOI OAFlux Project of Woods Hole Oceanographic Institution (http://oaflux.whoi.edu). The OSCAR currents were provided by NOAA’s Ocean Surface Current Analyses Real Time (http://www.oscar.noaa.gov/index.html). The ORA-S3 wind stress was obtained from ECMWF (http://old.ecmwf.int). The OISST.V2 was provided by the NOAA Environmental Modeling Center (http://www.emc.ncep.noaa.gov). This work is supported by the Chinese Academy of Sciences (XDA11010103, XDA11010203), the National Natural Science Foundation of China (41506019, 41525019, 41521005, 41176024), and the CAS/SAFEA International Partnership Program for Creative Research Teams.
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