Probabilistic Forecasts of Sea Ice Trajectories in the Arctic: Impact of Uncertainties in Surface Wind and Ice Cohesion

We evaluate the impact of uncertainties in surface wind and sea ice cohesion on sea ice forecasts by the neXtSIM sea ice model. neXtSIM includes the Maxwell-elasto-brittle rheology describing the ice dynamics. Ensemble forecasts are done every 10 days from January to April 2008. The ensembles are generated by perturbing the wind forcing and ice cohesion field both separately and jointly. The wind forcing, an external forcing of the model, is perturbed continuously during the forecast. While the sea-ice cohesion, an internal parameter of the model, is randomized on the initial field of each sea ice forecast. The model uncertainties are assessed statistically using ensemble forecasts, in which virtual drifters are seeded over the Arctic Ocean. We analyze the spread of Lagrangian sea ice trajectories of the ensemble of virtual drifters and compare them with the IABP buoys. We demonstrate that the wind perturbations usually contribute more to the forecast uncertainty, but the ice cohesion perturbations significantly increase the degree of anisotropy in the spread and become occasionally important during strong wind events.