Arctic sea-ice extent has declined over the past few decades with the greatest reduction occurring in late summer. The current generation of climate models predict that global warming may make the Arctic virtually ice free in summer towards the end of the century. When sea ice retreats, the atmosphere becomes exposed to the warm ocean underneath. As a result, heat fluxes from the ocean are allowed to warm the atmosphere. The largest anomalous heat fluxes are during winter when the air temperature is coolest relative to the ice and open water. The greatest sea-ice reduction is in late summer but this has little impact on the atmosphere, as the change in heat fluxes is small.
In this study, simulations show that the large heat fluxes during winter reduces storminess over the Barents Sea, Labrador Sea and northern Russia. However, a substantially larger reduction in North Atlantic storminess was found in March. The study shows that this was the only time when the complex feedback processes associated with the negative phase of the North Atlantic Oscillation (NAO) were triggered. The NAO is a pattern that represents shifts in the strength and direction of westerly winds and storminess across the North Atlantic. A negative NAO gives less rainfall and colder temperatures over northern Europe.
That sea-ice anomalies are able to influence the NAO in late winter is unexpected since the heat fluxes from the ocean are in fact smaller than the rest of the winter. This indicates a potentially more important role of sea-ice anomalies for our weather in the transition between winter and spring than what has been thought before.
To isolate the impact of a new seasonal cycle of sea ice, this study uses simulations of the atmospheric climate model ECHAM5 developed at the Max-Planck-Institute for Meteorology. Simulations were carried out using a present-day sea-ice cover and a new seasonal cycle projected for the end of the century.
Weaker storminess in late winter
A new paper published in Climate Dynamics shows that the isolated effect of a reduced Arctic sea-ice cover will lead to weaker North Atlantic storminess in late winter.
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