The simulation of the Arctic sea-ice cover with coupled atmosphere-ocean-sea ice models still comprises large uncertainties, which are very likely attributable to poor representation of feedback processes between the atmosphere and ocean-sea ice components of the coupled models. One of the major processes for the sea-ice retreat during the Arctic summer is the ice-albedo feedback. Due to the combination of improved parameterizations for ice growth, ice albedo, and snow cover on ice, a more realistic representation of this feedback process in the coupled regional climate model HIRHAM-NAOSIM has been achieved, by which the simulation of the summertime sea-ice extent is significantly improved.Ensemble simulations with the improved version of HIRHAM-NAOSIM show that the interannual variability of the sea-ice cover is associated with differences in the atmospheric circulation. A realistic simulation of the atmospheric circulation is a necessary, but not sufficient prerequisite for the reproduction of the observed sea-ice extent in summer. The ensemble simulations also demonstrate that internal variability is important in summer, whereas the external atmospheric forcing of the regional model system dominates the interannual variability in winter. Furthermore, there are indications that the large-scale atmospheric forcing induces a pronounced multi-decadal variability in sea-ice volume, with rather thin ice in the 1950s and 1960s and thick ice in the 1980s and 1990s. However, the coupled model is still not able to reproduce the observed downward trend in summer ice extent. The contact with reality of the multi-decadal variability is therefore uncertain.
Helmholtz Research Programs > PACES I (2009-2013) > TOPIC 4: Synthesis: The Earth System from a Polar Perspective > WP 4.1: Current and Future Changes of the Earth System