Takanori Horii, Iwao Ueki, Kentaro Ando

Published in Journal of Geophysical Research: Oceans, NOV 2020

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 southesterly 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.

Fig. Correlation coefficients of satellite‐based precipitation with mixed layer salinity observed by Argo. The Argo salinity data for day −10 and day 0 during 11 upwelling events were used (sampling number: 22). Red circles indicate locations of observed coastal upwelling events. The precipitation data were smoothed with a 5‐day running mean filter before computation. The coefficients exceeding 0.352, 0.413, and 0.526 are statistically significant at the 90%, 95%, and 99% levels, respectively.

Horii, T., Ueki, I., & Ando, K. (2020). Coastal upwelling events, salinity stratification, and barrier layer observed along the southwestern coast of Sumatra. Journal of Geophysical Research: Oceans, 125, e2020JC016287. https://doi.org/10.1029/2020JC016287