Turbulent kinetic energy and its dissipation rate in the equatorial mixed layer

The authors apply a one-dimensional mixed layer model, based on second mome nt closure of turbulence, to study the characteristics of turbulence in the equatorial mixed layer. In particular, they focus on characteristics such as the TKE and the dissipation rate in the upper layers of the equatorial o cean, especially the phenomenon of deep episodic penetration well below the mixed layer of elevated dissipation rates commonly observed in microstruct ure measurements in the central tropical Pacific. Model simulations for the Tropic Wear experiments in 1984 and 1987 and Tropical Instability Wave Exp eriment in the central Pacific as well as the Tropical Oceans Global Atmosp here Coupled Ocean-Atmosphere Response Experiment (TOGA COARE) Intensive Op erating Period (IOP) observations in the western Pacific warm pool are perf ormed. Modeled dissipation rates are found to be in reasonable agreement wi th their measured by microstructure profilers during these observations. Se nsitivity studies are carried out to investigate the mechanisms underlying the deep penetration process. The authors find that the deep penetration of turbulence arises simply due to the instability and mixing resulting from the background vertical shear of the Equatorial Undercurrent enhanced by th e easterly winds. The process is present whether or nor there is nocturnal cooling. Deep penetration of turbulence is absent during westerlies, and th en the behavior of the equatorial mixed layer is more like that of a high-l atitude mixed layer. The modeled dissipation rates in the tropical western Pacific warm pool are in agreement with values observed during the TOGA COA RE IOP. Both TKE and dissipation rates are significantly elevated in the mi xed layer during westerly wind bursts. However, because of the weak backgro und shear due to an undercurrent that is tao weak and too deep in this regi on, turbulent mixing does not penetrate much below the mixed layer in the w arm pool.