The Role of Double Diffusive Convection in the Mixing Process in the ocean

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1.In the area of the western-north Pacific ocean, detailed observations of temperature, salinity and turbulent dissipation using CTD and Turbomap in 2004 and 2005 showed enhanced mixing processes might be due to double diffusive convection occurred in the area where typical water masses were contacted. Especially, off the Sanriku coast, double diffusive interleaving processes having high turbulent dissipation rate at the interfaces were observed from Thrbomap yo-yo observation.2.Simple one-dimensional temperature-salinity diffusion model parameterizing the vertical eddy diffusivities changing with density ratio were employed to investigate the development of vertical temperature and salinity profiles typically observed in the north Atlantic. We first successfully showed the formation of step structure caused by the convergence of density flux due to double diffusive convection. These steps having small vertical scale at first, merges to increase their thickness, and finally approaches smooth temperature and salinity profiles with the density ratio value 2. This final state is coincided with the observation.3.Mapping of density ratio in the world ocean from WOCE data set has been continued. In the course of this study, vertical eddy diffusivities are estimated through the density flux ratio due to double diffusive convection. We obtained 1 Munk (10^<-4>m^2/s) in the whole Atlantic Ocean and in the area around Antarctic Circumpolar Current. But, in the Pacific Ocean, the value was 10^<-6>m^2/s〜l0^<-5>m^2/s at most. These latter values are not sufficient to maintain the permanent thermocline, but the effect of double diffusive convection is not negligible for this process.