The Atmospheric Response to Realistic Reduced Summer Arctic Sea Ice Anomalies

The impact of reduced Arctic summer sea ice on the atmosphere is investigated by forcing an atmospheric general circulation model, the Community Climate Model (CCM 3.6), with observed sea ice conditions during 1995, a low-ice year. The 51 experiments, which spanned April to October of 1995, were initiated with different states from a control simulation. The 55-year control was integrated using a repeating climatological seasonal cycle of sea ice. The response was obtained from the mean difference between the experiment and control simulations. The strongest response was found during the month of August where the Arctic displays a weak local thermal response, with warmer surface air temperatures and lower sea level pressure (SLP). However, there is a significant remote response over the North Pacific characterized by an equivalent barotropic (anomalies are collocated with height and increase in magnitude) structure, with anomalous high SLP collocated with a ridge in the upper troposphere. The ice anomalies force an increase (decrease) in precipitation north of (along) the North Pacific storm track. A linear baroclinic model forced with the transient eddy vorticity fluxes, transient eddy heat fluxes, and diabatic heating separately demonstrated that transient eddy vorticity fluxes are key to maintaining the anomalous high over the North Pacific. The model's sensitivity to separately imposed ice anomalies in the Kara, Laptev-East Siberian, or Beaufort seas includes SLP, geopotential height, and precipitation changes that are similar to but weaker than the response to the full sea ice anomaly.