Abstract

The vertical mixing structure induced by double diffusion under equal-density stratification conditions was investigated through numerical simulations. A Fortran-based numerical model was developed to account for the differing molecular diffusion coefficients of heat and salt, employing a non-hydrostatic two-dimensional vertical cross-sectional framework. The simulation results were subsequently visualized using Python to examine the temporal evolution of temperature, salinity, and density distributions. During the initial stage, thermal diffusion proceeded more rapidly than saline diffusion, leading to temperature perturbations in the vicinity of the density interface. The results indicate that the differential diffusion of heat and salt enhanced the spatial variability of the density structure, thereby promoting the gradual development of vertical mixing. Overall, this study provides an intuitive understanding of the temporal evolution of a two-layer stratified ocean system by visually demonstrating the vertical mixing process driven by double diffusion. The findings are expected to support prospective teachers as well as middle and high school students in developing a clearer conceptual understanding of density variations in seawater arising from differences in temperature and salinity.