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.