Impacts of South China Sea throughflow on the mean state and El Niño/Southern Oscillation as revealed by a coupled GCM

Abstract

The South China Sea (SCS) throughflow (SCSTF) enters the SCS from the Luzon Strait and exits it through the straits to the south. Using a coupled general circulation model (CGCM), this study reveals impacts of the SCSTF on the mean state and El Nino/Southern Oscillation (ENSO). It is found that the model’s sea surface temperature becomes cooler in the eastern and far western equatorial Pacific and south of Japan, but significantly warmer in the SCS, when the SCSTF is blocked. The warming in the SCS is likely a result of accumulated surface heat flux which otherwise would be transported out of the SCS by the SCSTF. Furthermore, the dominant period of ENSO is 4 years when the SCSTF is allowed, but it becomes 5 years when the SCSTF is blocked. This is because the meridional extent of zonal wind anomalies becomes broader and the Walker Circulation in the Indian Ocean becomes stronger in the no-SCSTF case. On the other hand, changes in the zonal location of zonal wind anomalies, the phase speed of baroclinic Kelvin waves, the occurrence of westerly wind bursts, and strength of atmospheric feedbacks do not contribute to the difference between the two experiments even though they are known to influence the ENSO period. The climatic importance of the SCSTF has been so far overlooked because of its small volume transport compared with other major currents in the global ocean, but the present work shows for the first time its possible impacts on ENSO.