Southern hemisphere climate system recovery from instantaneous sea ice removal

A coupled atmosphere-sea-ice model has been used to investigate the temporal response to instantaneous Antarctic sea-ice removal under the present external climate conditions. In all cases the system was seen to be transitive, in that the sea ice eventually grew back to the present climate conditions. Here we examine the timescale and nature of the ice and atmospheric relaxation back to 'control' conditions. Several experiments were carried out, either supposing that all the sea ice was removed at certain times of year, or that it was removed only over certain large areas. The model in each case was run for six realizations for the equivalent of several years to a new equilibrium. For the 'whole sea-ice removal' experiment the maximum impact was found to occur when the removal was made at the time of sea-ice maximum (September) and least reaction near the minimum. In both cases the return to normal occured by the middle of the following winter. The atmospheric responses comprised reduced surface pressure over the area from which ice had been removed, greatly increased turbulent fluxes, reduced difference between precipitation and evaporation (P - E) over the ocean and increased (P - E) over the Antarctic continent. The air temperature changes spread through the troposphere and tended to reduce the circumpolar westerlies north of and over the sea-ice zone. The reaction to the regional sea-ice removals was more local and depended on where the region was located relative to the mean circulation pattern around and over Antarctica.