Models of the upper ocean (usually one-dimensional) that take advantage of the concept of a mixed layer by assuming 1) the mean temperature, salinity, and horizontal velocity are quasi-uniform within the mixed layer; and 2) a quasi-discontinuous distribution (jump) exists for the same variables just below the mixed layer. This permits integrating the momentum and tracer equations from the bottom of the mixed layer to the surface to get equations for the bulk mixed layer velocity, temperature, and salinity, and adding an equation for the evolution of the mixed-layer depth derived from the vertically integrated (across the mixed layer) turbulence kinetic energy (TKE) equation.