Modulating surface heat flux through sea ice leads improves Arctic sea ice simulation in the coupled EC-Earth3

Abstract. In this study, we address a persistent positive bias in Arctic sea ice (concentration and thickness) in the global climate model EC-Earth3 (ECE3) by including a modulating factor to the surface sensible heat flux over regions with sea ice concentrations above 70 %, so-called ECE3L. We performed two pairs of 50-year simulations with repeated seasonal cycles: one pair replicating a cold climate and the other a warmer climate, with the latter characterised by thinner ice and weaker atmospheric boundary layer stability during winter. We show that modified heat flux can significantly alter surface air temperatures in the Arctic, with no substantial impact on lower latitudes. The changes are more pronounced in the cold climate, particularly during Arctic winter. We extended our comparison to two CMIP6 historical ensembles in a transient climate (1980–2014). We found that the mean sea ice states in the changing climate for the ECE3 (ECE3L) ensemble mean closely resembled the mean states in the cold-climate experiment. However, the reduction in sea ice area and volume achieved by ECE3L was nearly four times greater in the cold climate experiment than in the transient climate, reflecting the diminishing role of sea ice leads in a changing climate with decreasing occurrences of stable stratification in winter. Finally, our comparisons with satellite observations and reanalysis datasets demonstrated that ECEL3 significantly improves the local amplification ratio in the marginal ice zone of the Arctic, underscoring the importance of atmospheric stability shaped by central Arctic pack ice and its impact on Arctic amplification.