A28. Numerical challenges in representing isopycnal mixing on a regular grid

Title

Numerical challenges in representing isopycnal mixing on a regular grid

Authors

Anand Gnanadesikan (gnandes@jhu.edu) and Marie-Aude Pradal

Abstract

Mixing along isopycnals in the ocean is much stronger than mixing across these surfaces- with tracer spreading hundreds of km laterally while moving only 20-30 m vertically. However, there is a fundamental challenge in enforcing this constraint on regular Cartesian grids, where fluxes are either in the vertical or horizontal directions. In order to ensure that the net flux across an isopycnal is zero, downgradient fluxes in one direction are always balanced with upgradient fluxes in another. Such upgradient fluxes can result in the creation of spurious minima and maxima and even (in some idealized cases when combined with biological cycling) in the generation of instabilities. In this poster we explore whether allowing mixing between different levels of adjacent columns can improve this problem and under what conditions it does so.