An improved model for the oceanic boundary layer is presented in view of the recent observation of the microstructure of the upper ocean including the high dissipation rate near the sea surface. In the new model the surface boundary conditions for both the turbulent kinetic energy flux and the roughness length scale are modified. The parameterization of stratification effects on turbulence is improved, and the convective process is reformulated on the basis of the observation of uniform temperature and velocity profiles within the convective mixed layer. Evolutions of the profiles of both the dissipation rate and temperature of the observation data Patches Experiment as well as the time series of the sea surface temperature over the observation days, are successfully simulated during a diurnal cycle for the first time. It is also shown that the model reproduces various important features of the oceanic boundary layer, for example, the formation of a diurnal thermocline, the profiles of buoyancy flux, and the magnitudes of the buoyancy gradients both within the mixed layer and at the diurnal thermocline. Performance of the model is compared with that of the widely used Mellor-Yamada model. ¿ 1999 American Geophysical Union