Refraction of the M2 internal tides by mesoscale eddies in the South China Sea

Abstract

Mesoscale eddies (MEs) are active in the northern South China Sea, yet it is hard to separate their impacts on the internal tides (ITs) from those of other subtidal circulation. This study examines the role of an anticyclonic eddy and a cyclonic eddy in modulating the M2 ITs based on numerical simulations. In idealized experiments, MEs that differ only in polarity are located on the main beam of the M2 ITs in the northern South China Sea. Results show that the anticyclonic eddy and cyclonic eddy cause northward and southward refractions of the M2 ITs, respectively, which echoes the realistic simulation. The most dramatic changes in the M2 IT energy fluxes occur on the continental slope to the west of the MEs. Theoretical analysis based on the ray-tracing model and the empirical model for estimating wave front locations reveals that the MEs cause refraction of the M2 ITs by changing the phase speeds. Further investigation shows that the currents related to the MEs make a greater contribution to the IT refraction than the ME-associated stratification. These results have important implications for investigation of spatial and temporal variations in the magnitude and direction of the M2 IT energy fluxes.