On the calculation of normalized viscous-plastic sea ice stresses

• Main Authors: Lemieux, Jean-François, Dupont, Frédéric
• Format: Text
• Language: English
• Published: 2019
• Subjects: Sea ice
• Online Access: https://doi.org/10.5194/gmd-2019-284; https://www.geosci-model-dev-discuss.net/gmd-2019-284/

Calculating and plotting the normalized states of stress for viscous-plastic sea ice models is a common diagnostic for evaluating the numerical convergence and the physical consistency of a numerical solution. Researchers, however, usually do not explain how they calculate the normalized stresses. Here, we argue that care must be taken when calculating and plotting the normalized states of stress. A physically consistent and numerically converged solution should exhibit normalized stresses that are inside (viscous) or on (plastic) the yield curve. To do so, two possible mistakes need to be avoided. First, to assess the numerical convergence of a solution, one must compute the viscous coefficients and replacement pressure from the previous numerical iterate and the remaining strain rates from the latest iterate. Calculating the stresses only from the latest iterate falsely indicates that the solution has numerically converged. Second, the stresses should be normalized by the ice strength and not by the replacement pressure. Using the latter, one obtains converged states of stress that lie only on the yield curve (i.e., falsely indicating there are no viscous states of stress).