Coastal upwelling along the southwestern coast of Sumatra is a seasonal
upwelling that occurs in areas of high sea surface temperature and
abundant precipitation at the southeastern edge of the Indian Ocean warm
pool. Based on observations from two Argo floats that drifted and stayed
around Sumatra, we investigated ocean temperature and salinity
variations during several coastal upwelling events observed in
2013--2017. The Argo floats observed the vertical structure of
temperature and salinity every 10 days within 100 km from the
southwestern coast of Sumatra. The observation data show
intraseasonal-scale subsurface temperature cooling events with
significant upward displacements of the thermocline and high-salinity
water, led by anomalous local southwesterly winds and equatorial
easterly winds. During the coastal upwelling events, salinity
stratification and a thick barrier layer related to local precipitation
were also observed. Surface mixed layer temperature cooling were
relatively small in contrast to the significant subsurface anomalies. It
was found that during the coastal upwelling events, subsurface
cold-water upwelling signals did not necessarily reach the mixed layer
when salinity stratification and a thick barrier layer were present. The
implications of these observational results for understanding the local
atmosphere ocean interaction, and hence the occurrence of the Indian
Ocean Dipole, are discussed.