TURBULENCE AND STRATIFICATION ON THE TROPICAL OCEAN GLOBAL ATMOSPHERECOUPLED OCEAN-ATMOSPHERE RESPONSE EXPERIMENT MICROSTRUCTURE PILOT CRUISE

On the Tropical Ocean-Global Atmosphere-Coupled Ocean-Atmosphere Respo nse Experiment pilot cruise, at 147 degrees E, in the western Pacific Warm pool, we profiled for 17 days at 0 degrees N and for 5 days at 2 degrees N. Winds were generally light and variable in direction, but r ainfall was often quite intense. Contrary to what is seen in the centr al equatorial Pacific, we did not observe a deep diurnal cycle in diss ipation extending below the mixed layer. Strong daytime restratificati on often prevented nightly convective deepening down to the seasonal t hermocline, resulting in surface forcing remaining trapped in a shallo w layer. The relaxation of horizontal density gradients into vertical appears to be an important process driving restratification. Turbulent fluxes in the bottom of the mixed layer were generally small. Followi ng rainfall, we observed pools of fresh water that typically disappear ed within a few hours, leaving the mixed layer nearly homogeneous in s alinity; thus we did not observe a permanent barrier layer. Modeling s uch events using the Price-Weller-Pinkel model suggests a fresh pool w ill be mixed away on timescales of a few days, primarily by nighttime convection. The observed vertical structure can be accounted for by lo cal vertical mixing processes.