Northern Hemisphere winter climate variability: Response to North American snow cover anomalies and orography

Abstract

Links between autumn-winter snow anomalies over North America and winter climate parameters throughout the Northern Hemisphere are examined. GCM integrations are performed from September through February, with prescribed snow forcings over North America (NA) reflecting realistic, observed high/low autumn snow conditions. Forty-member ensemble differences reveal robust responses in surface air temperature and sea level pressure (SLP) fields. Over NA a negative temperature/positive SLP response occurs while over Europe a positive temperature/negative SLP response emerges. Additionally, a dynamic wave response occurs in the troposphere, across NA and extending downgradient into Eurasia. The contribution of North American (NA) orography is evaluated via an additional pair of experiments in which mountains are removed. The resulting climatic response is mitigated considerably, which suggests a nonlinear coupling of thermal and mechanical forcings. Finally, possible physical pathways for the remote response are hypothesized, involving dynamical mechanisms consistent with previous studies. Copyright 2007 by the American Geophysical Union.