Characteristics and mechanisms of the intraseasonal variability of sea surface salinity in the southeastern Arabian Sea during 2015–2020

Based on Soil Moisture Active Passive sea surface salinity(SSS) data from April 2015 to August 2020, combined with Objectively Analyzed Air-Sea Heat Flux and other observational data and Hybrid Coordinate Ocean Model(HYCOM) data, this work explores the characteristics and mechanisms of the intraseasonal variability of SSS in the southeastern Arabian Sea(SEAS). The results show that the intraseasonal variability of SSS in the SEAS is very significant, especially the strongest intraseasonal signal in SSS, which is located along the northeast monsoon current(NMC) path south of the Indian Peninsula. There are remarkable seasonal differences in intraseasonal SSS variability, which is very weak in spring and summer and much stronger in autumn and winter. This strong intraseasonal variability in autumn and winter is closely related to the Madden-Julian Oscillation(MJO) event during this period. The northeast wind anomaly in the Bay of Bengal(BOB) associated with the active MJO phase strengthens the East India Coastal Current and NMC and consequently induces more BOB low-salinity water to enter the SEAS, causing strong SSS fluctuations. In addition, MJO-related precipitation further amplifies the intraseasonal variability of SSS in SEAS. Based on budget analysis of the mixed layer salinity using HYCOM data, it is shown that horizontal salinity advection(especially zonal advection) dominates the intraseasonal variability of mixed layer salinity and that surface freshwater flux has a secondary role.