Sea surface salinity variability during the Indian Ocean Dipole and ENSO events in the tropical Indian Ocean

Abstract

An ocean reanalysis that covers the period from 1871 to 2008 is used to analyze the interannual variability of sea surface salinity (SSS) in the tropical Indian Ocean. The reanalysis SSS and the SSS anomaly patterns during Indian Ocean Dipole (IOD) and El Niño–Southern Oscillation (ENSO) events are compared with patterns from Argo SSS data. The mean seasonal SSS variation is large in the northern Bay of Bengal compared with variations in the Arabian Sea and equatorial Indian Ocean. During a positive IOD event, positive SSS anomalies are found along the Sumatra coast that are due to the combination of wind‐driven upwelling of subsurface high‐salinity waters, enhanced evaporation, and anomalous surface circulation. The opposite is true, to a lesser extent, during negative IOD events. A dipole mode index for salinity (DMIS) based on SSS data and a new index based on the average of salinity in a region off the coast of Sumatra are introduced to monitor SSS variability during IOD and ENSO events. The impact of concomitant El Niño events on a positive IOD event is large with freshening (a negative SSS anomaly) in the equatorial Indian Ocean and salting (positive SSS anomaly) off the southern Sumatra coast. The (impact of) intense freshening reaches into the southwestern tropical Indian Ocean. The impact of concomitant La Niña with negative IOD is also large with an intense freshening in the southeastern Arabian Sea and salting off the northern Sumatra coast.

Role of El Niño Southern Oscillation (ENSO) Events on Temperature and Salinity Variability in the Agulhas Leakage Region

“…This paper relied primarily on AVHRR SST and SODA SSS. Both data sets have been used in countless previous studies to explore the Indian Ocean basin or Agulhas current system and have been proven reliable for doing so [23,25]. However, it is important to note some issues with these data sets that may have influenced the results.…”

“…Primarily, easterly (westerly) winds drive upwelling (downwelling) along the Sumatra coast, explaining the observed secondary signal of positive (negative) SSS anomalies further enhanced by reduced (increased) rainfall created from the atmospheric circulation patterns of El Niño (La Niña). The negative primary SSS signal observed in the equatorial Indian Ocean during El Niño is explained by horizontal advection of low salinity waters from the Bay of Bengal, while the primary positive SSS in the equatorial Indian Ocean during La Niña is produced by eastward-flowing Wyrtki jets [23].…”

“…The previous basin-wide trend in SST is isolated near the region east of Madagascar at~15 • -35 • S. Note, this is the latitude where the SEC is found [15], supporting the idea that the SEC is involved in signal transmission. Grunseich et al [23] attributes the westward movement of the SSS signal to Rossby waves associated with the westward flowing SEC. Most importantly, the SST signal and primary SSS signal surround Madagascar to interact with the source currents, which has the potential to influence eddy formation of the EMC and MC, thus continuing on to impact Agulhas leakage.…”

Implications of North Atlantic Sea Surface Salinity for Summer Precipitation over the U.S. Midwest: Mechanisms and Predictive Value

“…Our results are consistent with previous studies that focus on the impact of ENSO and NAO on SSS. The ENSO influence on SSS is mainly over the tropical Pacific and tropical north Indian Ocean but is much less over the North Atlantic (Gouriou and Delcroix 2002;Grunseich et al 2011). In addition, the NAO mainly influences the SSS during winter seasons and is confined to the midlatitudes (Mignot and Frankignoul 2003).…”

Impacts of the IOD-associated temperature and salinity anomalies on the intermittent equatorial undercurrent anomalies

“…It was argued that the salinity anomalies may have a very important impact on the EUC during the 1997 IOD event (Masson et al 2004). This is probably because the anomalous zonal currents driven by the easterlies advect the fresh water from the Bay of Bengal and the Sumatra-Java coast into the central equatorial Indian Ocean to change the seawater density distribution (Thompson et al 2006;Grunseich et al 2011;Zhang et al 2013;Li et al 2016). For example, Masson et al (2003Masson et al ( , 2004 designed sensitivity experiments to investigate the impacts of salinity on the pressure gradient and vertical mixing and concluded the importance of the IOD-deduced salinity anomalies to the EUC.…”