Impacts of a mesoscale eddy pair on internal solitary waves in the northern South China Sea revealed by mooring array observations

Abstract

oth internal solitary waves (ISWs) and mesoscale eddies are ubiquitous in the northern South China Sea (SCS). In this study, we examine the impacts of mesoscale eddies on the ISWs transiting the northern SCS deep basin which evolve from the steepening internal tide generated in Luzon Strait, using in situ data collected from a specifically-designed mooring array. From November 2013 to January 2014, an energetic mesoscale eddy pair consisting of one anti-cyclonic eddy (AE) and one cyclonic eddy (CE) propagated across the mooring array. Observations revealed that the amplitude, propagation direction and speed of the trans-basin ISWs were significantly modulated by the eddy pair. When the moorings were covered by the southern portion of the AE, the ISW amplitudes decreased by as much as 67% due to the thermocline deepening along the wave direction and the energy divergence along the wave front. When the moorings were covered by the northern portions of both eddies, the amplitude of ISWs also decreased, but to a relatively smaller degree. ISWs propagated the fastest inside the southern portion of the AE, where both the thermocline deepening and eddy currents enhanced the propagation speed of ISWs. Under the influence of the AE (CE) core, ISWs propagated more northward (southward) than usual. The observational results reported here highlight the importance of resolving mesoscale eddies in circulation-internal wave coupled models to accurately predict kinematic characteristics of ISWs.