The Influence of Sudden Arctic Sea-Ice Thinning on North Atlantic Oscillation Events

Utilizing the Community Atmosphere Model, version 4 (CAM4), the influence of sudden Arctic sea-ice thinning on North Atlantic Oscillation (NAO) events is investigated on a sub-seasonal time scale. First, the control simulation with CAM4 using prescribed daily boundary conditions produces realistic descriptions for the frequency and evolution of NAO events. Second, sensitivity experiments are then conducted to investigate the impact of sudden Arctic sea-ice thinning on NAO events. Numerical results show that the NAO has obvious responses to sudden sea-ice thinning over 10 days. Finally, the NAO responses to sudden sea-ice thinning are related to the positions of the NAO event. Further diagnostic analysis reveals that when the poleward centre of a positive NAO event is located west (east) of Greenland, cold (warm) advection would be induced because of the sudden sea-ice thinning along with the northward (southward) wind. This cooling (warming) causes the air to contract (expand) and further results in a decrease (increase) in the geopotential height and sea level pressure fields, which corresponds to a positive NAO (negative NAO) response. The results of this investigation show that the response of atmospheric circulation to boundary conditions is determined by both boundary condition changes and the atmospheric circulation regime, which provides an understanding of the effect on an NAO event of sudden sea-ice thinning on a sub-seasonal time scale.