Abstract. The Sea Ice Evaluation Tool (SITool) described in this
paper is a performance metrics and diagnostics tool developed to evaluate
the skill of Arctic and Antarctic model reconstructions of sea ice
concentration, extent, edge location, drift, thickness, and snow depth. It
is a Python-based software and consists of well-documented functions used to
derive various sea ice metrics and diagnostics. Here, SITool version 1.0
(v1.0) is introduced and documented, and is then used to evaluate the
performance of global sea ice reconstructions from nine models that provided
sea ice output under the experimental protocols of the Coupled Model
Intercomparison Project phase 6 (CMIP6) Ocean Model Intercomparison Project with
two different atmospheric forcing datasets: the Coordinated Ocean-ice
Reference Experiments version 2 (CORE-II) and the updated Japanese 55-year
atmospheric reanalysis (JRA55-do). Two sets of observational references for
the sea ice concentration, thickness, snow depth, and ice drift are
systematically used to reflect the impact of observational uncertainty on
model performance. Based on available model outputs and observational
references, the ice concentration, extent, and edge location during
1980–2007, as well as the ice thickness, snow depth, and ice drift during
2003–2007 are evaluated. In general, model biases are larger than
observational uncertainties, and model performance is primarily consistent
compared to different observational references. By changing the atmospheric
forcing from CORE-II to JRA55-do reanalysis data, the overall performance
(mean state, interannual variability, and trend) of the simulated sea ice
areal properties in both hemispheres, as well as the mean ice thickness
simulation in the Antarctic, the mean snow depth, and ice drift simulations
in both hemispheres are improved. The simulated sea ice areal properties are
also improved in the model with higher spatial resolution. For the
cross-metric analysis, there is no link between the performance in one
variable and the performance in another. SITool is an open-access
version-controlled software that can run on a wide range of CMIP6-compliant
sea ice outputs. The current version of SITool (v1.0) is primarily developed
to evaluate atmosphere-forced simulations and it could be eventually
extended to fully coupled models.