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The Conductivity–Temperature–Depth (CTD) and acoustic Doppler current profiler (ADCP) measurements along 18°N off the western Luzon in the South China Sea (SCS), collected during a cruise from August 12–14, 2012, were used to explore the vertical structure of an anticyclonic eddy (AE) during the observational period. Further, the French Archiving, Validation and Interpretation of Satellite Oceanographic data (AVISO) sea level anomaly (SLA) and corresponding anomalous surface geostrophic velocity were used to study the temporal evolution of the AE. The vertical structure of the AE along 18°N in August 2012 showed a trough located near 117.5°E. The AE extended vertically downward and its distinct feature was identifiable to 200 m depth. Seasonal variations of SLA indicate that the AE lasted for 5 months (June to early November), going through the growth and nearly stationary period from mid-June to late August and then propagating westward along 18°N with varying phase speeds and shapes to the continental slope off the southeastern Hainan Island during late September to November. Furthermore, T–S characteristics suggest that the AE was generated off the western Luzon. Interannual variations of the summer (July–September) SLA presented by Empirical Orthogonal Function analysis, indicates that the local circulation was enhanced by the anomalous anticyclonic eddy along 18°N in the years of 2008, 2010, 2012 and 2013 during the period from1993 to 2014. [ABSTRACT FROM AUTHOR]

• Passing eddy center (edge), ISW amplitude is damped to nearly 0 (increased by 50%). • Background current at the eddy center (edge) damps (amplifies) ISW amplitude. • Different effects caused by eddy near eddy edge make ISW amplitude change largely. Internal solitary waves (ISWs) were observed by mooring data in the South China Sea in August and September 2014. Normally the arrival pattern of ISWs is relatively regular and the ISW amplitudes have a positive correlation with the magnitude of semidiurnal tidal currents near the Luzon Strait. However, the ISW amplitudes observed in the second spring tide of September are significantly large when an anti-cyclonic eddy is passing the mooring. 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 varied 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 the eddy edge may damp or amplify the ISW amplitude. [ABSTRACT FROM AUTHOR]