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

1.2004年和2005年在西北太平洋海域利用CTD和Turbomap对温、盐和湍流耗散的详细观测表明，在典型水团接触的区域，由于双扩散对流的作用，混合过程增强。特别是在三陆海岸附近，Thrbomap yo-yo观测到了具有高湍流耗散率的双扩散交错过程。2.利用简单的一维温度-盐度扩散模型研究了北大西洋典型的垂直温度和盐度剖面的发展。我们首次成功地证明了由于双扩散对流引起的密度通量收敛所导致的台阶结构的形成。这些阶跃起初垂向尺度较小，随后逐渐合并，厚度逐渐增加，最后趋于密度比为2的光滑温盐剖面。3.继续利用WOCE数据进行全球海洋密度比制图。在这项研究的过程中，垂直涡动扩散率估计通过密度通量比由于双扩散对流。在<-4>整个大西洋和南极绕极流附近获得了1个Munk（10^ m^2/s）。但是，在太平洋，该值最多为10^<-6>m^2/s ~ 10 ^<-5>m^2/s。后者的值不足以维持永久温跃层，但双扩散对流的影响对于该过程来说是不可忽视的。

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.