Turbulent structure in the upper layer of the western Equatorial Pacific Ocean

The Richardson number dependence of vertical eddy diffusion coefficients in the western Equatorial Pacific Ocean was examined on the basis of a Microstructure Profiler (MSP) observations during the cruise of Natsushima (JAPACS-89). The Richardson numberR _i was estimated by using the mean shear of velocity profile measured by an Acoustic Doppler Current Profiler (ADCP) with the vertical interval of 15 meters within one or two hours of the each MSP cast. The raw data plot of the vertical eddy diffusion coefficientK _p shows a large scatter with increasing tendency belowR _i =0.5. The relation between the mean vertical eddy diffusion coefficientK _p and the Richardson numberR _i , averaged over every 0.025 in theR _i , supports the model of Pacanowski and Philander (1981) in the range ofR _i >0.5, but coincides with the result of Peterset al. (1988) in the range ofR _i <0.5.