Geoscientific Model Development | 2021
SITool (v1.0) – a new evaluation tool for large-scale sea ice simulations: application to CMIP6 OMIP
Abstract
Abstract. The Sea Ice Evaluation Tool (SITool) described in this\npaper is a performance metrics and diagnostics tool developed to evaluate\nthe skill of Arctic and Antarctic model reconstructions of sea ice\nconcentration, extent, edge location, drift, thickness, and snow depth. It\nis a Python-based software and consists of well-documented functions used to\nderive various sea ice metrics and diagnostics. Here, SITool version 1.0\n(v1.0) is introduced and documented, and is then used to evaluate the\nperformance of global sea ice reconstructions from nine models that provided\nsea ice output under the experimental protocols of the Coupled Model\nIntercomparison Project phase\xa06 (CMIP6) Ocean Model Intercomparison Project with\ntwo different atmospheric forcing datasets: the Coordinated Ocean-ice\nReference Experiments version 2 (CORE-II) and the updated Japanese 55-year\natmospheric reanalysis (JRA55-do). Two sets of observational references for\nthe sea ice concentration, thickness, snow depth, and ice drift are\nsystematically used to reflect the impact of observational uncertainty on\nmodel performance. Based on available model outputs and observational\nreferences, the ice concentration, extent, and edge location during\n1980–2007, as well as the ice thickness, snow depth, and ice drift during\n2003–2007 are evaluated. In general, model biases are larger than\nobservational uncertainties, and model performance is primarily consistent\ncompared to different observational references. By changing the atmospheric\nforcing from CORE-II to JRA55-do reanalysis data, the overall performance\n(mean state, interannual variability, and trend) of the simulated sea ice\nareal properties in both hemispheres, as well as the mean ice thickness\nsimulation in the Antarctic, the mean snow depth, and ice drift simulations\nin both hemispheres are improved. The simulated sea ice areal properties are\nalso improved in the model with higher spatial resolution. For the\ncross-metric analysis, there is no link between the performance in one\nvariable and the performance in another. SITool is an open-access\nversion-controlled software that can run on a wide range of CMIP6-compliant\nsea ice outputs. The current version of SITool (v1.0) is primarily developed\nto evaluate atmosphere-forced simulations and it could be eventually\nextended to fully coupled models.\n