Biharmonic

The biharmonic coefficient

$\mathrm{J} = -\mathrm{K}\cdot \nabla C + \nabla_{h}\left( \kappa_4 \nabla_{h}^2 C \right)$

References

Delhez, E., & Deleersnijder, E. (2007). Overshootings and spurious oscillations caused by biharmonic mixing. 
Ocean Modelling, 17(3), 183-198. doi: 10.1016/j.ocemod.2007.01.002.