Characterization of Mixing at the Edge of a Kuroshio Intrusion into the South China Sea: Analysis of Thermal Variance Diffusivity Measurements

The Kuroshio occasionally carries warm and salty North Paci fi c Water into fresher waters of the South China Sea, forming a front with a complex temperature - salinity ( T-S ) structure to the west of the Luzon Strait. In this study, we examine the T-S interleavings formed by alternating layers of North Paci fi c Water with South China Sea Water in a front formed during the winter monsoon season of 2014. Using observations from a glider array following a freefl oating wave -powered vertical pro fi ling fl oat to calculate the fi ne -scale parameters Turner angle, Tu, and Richardson number, Ri, we identi fi ed areas favorable to double -diffusion convection and shear instability observed in a T-S interleaving. We evaluated the contribution of double -diffusion convection and shear instabilities to the thermal variance diffusivity, x , using microstructure data and compared it with previous parameterization schemes based on fi ne -scale properties. We discover that turbulent mixing is not accurately parameterized when both Tu and Ri are within critical ranges (Tu . 60; Ri , 1 = 4 ). In particular, x associated with salt fi nger processes was an order of magnitude higher (6.7 3 10 27 K 2 s 21 ) than in regions where only velocity shear was likely to drive mixing (8.7 3 10 28 K 2 s 21 ).