CHARACTERIZATION OF VERTICAL MIXING AT A TIDAL-FRONT ON GEORGES BANK

Studies of mixing were done at the northern flank of Georges Bank in t he summer and autumn of 1988. Two time-series of the evolution and int ensity of microstructure were examined over a tidal period in the cont ext of tidal forcing and the evolution of the density and velocity fie ld at the site. From the CTD, ADCP and microstructure observations (EP SONDE) on Georges Bank, several interesting features of the mixing pro cesses were found. High dissipation and diffusivity regions appear nea r the bottom of the Bank. Turbulence near the bottom is highest in int ensity and reaches farthest from the bottom at peak tidal how and dimi nishes in intensity and vertical extent as the how decreases. The thic kness of the bottom turbulent layer has its maximum value when the dow is strongest and the stratification is weakest. Characterization of t he dissipation rate and turbulent diffusivities in respect to buoyancy frequency N, current shear S, Richardson Number R(i) and epsilon/upsi lon N-2 was done. Dissipation and chi(T) showed little dependence on s hear or N-2 but decreased at larger R(i). chi(t) was found to be highe r in regions of higher N-2 and increased as epsilon/upsilon N-2 increa sed. K-T, K-rho and K-nu, were all highest near the bottom in excess o f 10(-2) m(2) s(-1) and decreased towards the surface. There was littl e suggestion of a dependence of mixing efficiency on S-2, R(i) or epsi lon/upsilon N-2, but some indication that Gamma decreases with decreas ing N-2. Copyright (C) 1996 Elsevier Science Ltd.