Observations of different effects of an anti-cyclonic eddy on internal solitary waves in the South China Sea

Internal solitary waves (ISWs) were observed by mooring data in the South China Sea in August and September, 2014. Although tidal forcings in the Luzon Strait are almost identical in these two months, the variation of ISW amplitudes observed in the neap tide of September is abnormally large due to the effect of an anti-cyclonic eddy. When an ISW passes the eddy center, its amplitude reduces to nearly zero, but when an ISW passes the eddy edge, its amplitude increases by 50%. A deepened thermocline always damps the ISW amplitudes, whilst the eddy-induced background currents at different locations may have contrary effects on the ISW amplitudes, e.g., the background current at the eddy center tends to damp the ISW amplitude but that at the eddy edge amplifies the ISW amplitude. The different effects of a deepened thermocline and eddy-induced background currents near eddy edge make the ISW amplitude change.