Modeled Climate State and Dynamic Responses to Anomalous North American Snow Cover

The radiative and thermal properties of widespread snow cover anomalies have the potential to modulate local and remote climate over monthly to seasonal time scales. In this study, physical and dynamical links between anomalous North American snow conditions and Northern Hemisphere climate are examined. A pair of 40-member ensemble AGCM experiments is run, with prescribed high- and low-snow forcings over North America during the course of an entire year (EY). The difference between the two ensemble averages reflects the climatic response to sustained EY snow forcing. Local surface responses over the snow forcing occur in all seasons, and a significant remote surface temperature response occurs over Eurasia during spring. A hemispheric-scale transient eddy response to EY forcing also occurs, which propagates downstream from the forcing region to Eurasia, and then reaches a maximum in extent and amplitude in spring. The evolution of this transient eddy response is indicative of considerable downstream development and is consistent with known storm-track dynamics. This transient response is shown to be a result of persistent steepened temperature gradients created by the anomalous snow conditions, which contribute to enhanced baroclinicity over the storm-track entrance regions. A second pair of experiments is run, with the prescribed high- and low-snow forcings over North America restricted to the fall season (FS). The dynamical response to FS forcing is muted compared to the EY scenario, suggesting that the seasonal timing and persistence of the snow forcing are essential for the remote teleconnection.