Coastal upwelling events, salinity stratification and barrier layer observed along the southwestern coast of Sumatra

Coastal upwelling along the southwestern coast of Sumatra during the boreal summer monsoon is closely linked to the El Nino/Southern Oscillation and the Indian Ocean Dipole. To understand the coastal upwelling system, we investigated ocean temperature and salinity variations obtained from Argo floats. During 2013-2017, two Argo floats observed vertical structure of temperature and salinity within 100 km from the southwestern coast of Sumatra. The floats observed intraseasonal-scale subsurface temperature cooling events with significant upward movements of thermocline. Together with the signals, anomalous southeasterly alongshore winds, equatorial easterly winds, and upward expansion of high-salinity water were also observed. These observational results indicate that the Argo floats observed the coastal upwelling signals along the southwestern coast of Sumatra. On the several events, the upwelling signals were accompanied by surface low salinity probably associated with local precipitation. The relationship of the local precipitation, surface-to-subsurface salinity stratification, barrier layer thickness, and mixed layer temperature variation observed during the coastal upwelling events are further presented.