Universality of the modeled small-scale response of the upper tropical ocean to squall wind forcing

The upper ocean response to idealized surface wind forcing that is represen tative of conditions observed during the TOGA-COARE Intensive Observation P eriod is studied by numerical simulations using a second moment closure mod el. A set of experiments is described with a variety of squall-like wind st ress distributions and linear initial stratification in the ocean. Several physical regimes of turbulent mixing and decay during and after wind forcin g are described. Differences in the structure of the upper and lower parts of the mixing layer are analyzed. The results indicate an exponential decay of turbulent kinetic energy (TKE) with lime after surface forcing is remov ed, and TKE source terms continue to play an important role. The velocity and density structure after the squall are found to be univers al, with a nearly constant Richardson number throughout the mixing layer. I t is demonstrated that this implies that the mixed layer depth is determine d by the initial buoyancy frequency and total momentum input from the wind stress in the same manner as in the bulk mixed layer models. It does not de pend essentially on the squall duration or the time evolution of the wind s tress during the squall.