Parameterization of vertical mixing in numerical models of tropical oceans.

Abstract

Measurements indicate that mixing processes are intense in the surface layers of the ocean but weak below the thermocline, except for the small region below the core of the Equatorial Undercurrent where vertical temperature gradients are small and the shear is large. Parameterization of these mixing processes by means of coefficients of eddy mixing that are Richardson-number dependent, leads to realistic simulation of the response of the equatorial oceans to different windstress patterns. In the case of eastward winds results agree well with measurements in the Indian Ocean. In the case of westward winds it is of paramount importance that the nonzero heat flux into the ocean be taken into account. This heat flux stabilizes the upper layers and reduces the intensity of the mixing, especially in the east. With an appropriate surface boundary condition, the results are relatively insensitive to values assigned to constants in the parameterization formula. (A)