Evaluating remedies for numerical mixing in a ¼° global NEMO configuration

Numerical mixing in fixed-coordinate ocean models such as NEMO is known to arise from several sources, including truncation errors in the advection scheme, leakage of the isoneutral explicit mixing into the dianeutral direction, and excessive entrainment of overflow waters, and this spurious mixing has been associated with significant drifts and biases in model simulations. We present results from an ensemble of ¼° forced NEMO simulations in which we investigate the sensitivity of the numerical mixing to various selections of numerical schemes and parameter settings in the model, including the z~ filtered ALE vertical coordinate, increased viscosity, changes in the order of tracer advection and the choice of isoneutral mixing schemes. We also discuss the sensitivity of numerical mixing to the choice of surface forcing product.