**Abstract:**

In the first part of this talk, double-diffusive interleaving is examined as it progresses from a linear instability towards finite amplitude. We examine the “finger” and “diffusive” instability types and ask whether a steady state is possible. We find that the strength of the fluxes across the “diffusive” interfaces must be many times stronger relative to the corresponding fluxes across the “finger” interfaces than is indicated from existing flux laws as derived from laboratory experiments. The total effect of the interleaving motion on the vertical fluxes of heat and of salt is calculated for the steady-state solutions.

The remainder of the talk proposes a method to address the limited spatial resolution of ocean models. Horizontal eddy fluxes of heat and other scalar quantities in the ocean are due to correlations between the horizontal velocity and tracer fields. However, the limited spatial resolution of ocean models means that these correlations are not fully resolved using the velocity and temperature evaluated on the model grid. We derive a method for estimating the horizontal flux due to spatially unresolved spatial correlations, based on calculating an additional non-divergent velocity to advect all scalar variables. The sum of the Eulerian-mean velocity and this extra advection we call the Horizontal Residual Mean velocity. The calculation of the extra advection is based on the depth-integrated horizontal transport from the seafloor to the density surface whose spatially averaged height is at the height of the calculation. We find that in the Southern Ocean this new HRM advection accounts for 0.2PW of meridional heat flux.

**Bio:**

Yuehua currently works as a research assistant at the School of Mathematics and Statistics, University of New South Wales. She has completed her Ph.D. degree of Applied Maths specialising in Physical Oceanography and Ocean Modelling.

Her research interests are in fluid dynamics, ocean mixing processes and ocean model improvement. During her Ph.D. studies, she investigated the steady state solutions for a double diffusive interleaving model which incorporated experimental interfacial flux laws. Moreover, she derived a method to approximate the spatial correlation induced water and tracer transports, which are often missed due to the limited spatial resolution of ocean models. She has also gained knowledge and skills in modifying ocean models and machine learning. Therefore, she is currently working on implementing her method, which calculates the spatial correlation induced transports, into Modular Ocean Model 6.

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