A regional view of the North Atlantic Oscillation

The Polar MM5 regional climate model is used to investigate some of the physical mechanisms that help to produce the wintertime climate response to the North Atlantic Oscillation (NAO) at high latitudes. Attention is given to the role of Greenland orographic effects in determining the position of the anomalous Icelandic low during the high phase of the NAO, and to the role of cloud radiative effects in producing the surface temperature response to NAO variability.; Greenland affects the Icelandic low in two ways. The ice sheet tends to weaken northward traveling baroclinic waves by limiting the potential for wave growth through baroclinic processes. Additionally, Greenland contributes to more frequent lee cyclogenesis during high NAO months that helps to maintain low pressure at high latitudes and to select the region southeast of Greenland as the location of the anomalous Icelandic low. These results are considered in light of recent evidence for rapid changes in Greenland's ice volume.; NAO polarity shifts are accompanied by cloud cover changes that have a strong impact on the surface radiation budget at high latitudes. Differences in surface cloud radiative forcing between high and low NAO months closely resemble the pattern of surface temperature change, suggesting that cloud cover changes may contribute to NAO-related surface temperature variability during the polar night. The cloud response at high northern latitudes to the NAO implies that simulated future changes in Arctic cloudiness may be fundamentally different in models that do and do not simulate long-term NAO trends, which could result in significant intermodel differences in regional climate change predictions.