Richardson number on the order of 0.5, much closer to the correct value of 

 0.25. For simplicity, the stability function ^ for salinity is assumed to be 

 the same as 41 for temperature. 



The eddy coefficients in the absence of any stratification are assumed to 

 be of the following form for Ay • 



A - "^ 







2 I / V o . V o1 5 



^0 H 



(ty^(t)l' (--) 



where A is a length scale. In general, A is assumed to be a parabolic 

 function of a with its peak value at mid-depth not exceeding a certain 

 fraction of the local depth. 



2 6 2 



Although lateral eddy coefficients (A^ - 10 to 10 cm /sec) are 



typically several orders of magnitude higher than the vertical eddy 



2 2 

 coefficients (A^ -1 to 10 cm /sec), the net effect of lateral turbulent 



diffusion is generally small compared to the lateral advection and vertical 



turbulent diffusion, except within the thin lateral boundary layers. 



Murthy (1976) found that the lateral mixing in the open waters of Lake Ontario 



increases with the size of the tracer cloud. With a cloud size of 1 km, his 



5 2 

 formula gives a lateral diffusion coefficient on the order of 10 cm /sec in 



the epilimnion, while a value two orders of magnitude smaller in the 



hypolimnion. Csanady (1963), on the other hand, measured a much smaller value 



2 

 of 400 cm /sec in the epilimnion under similar conditions. Numerical 



experiments in Lake Erie (Sheng, 1975) indicate that the lateral diffusion 



coefficient has little effect on the large scale circulation. 



For the first grid point above the bottom, the vertical diffusion terms 

 in Eqs. (2.42) and (2.43) contain the bottom shear stresses. A quadratic 

 stress law with a physically meaningful drag coefficient, as shown in Eqs. 

 (2.19) and (2.20), derived from boundary layer dynamics, is used. The 

 physical roughness of the coastal environment is correctly reflected in such a 

 formulation. 



43 



