Lott François author Robertson Andrew W. author Columbia University. International Research Institute for Climate and Society Ghil Michael author Columbia University. International Research Institute for Climate and Society originator text Articles 2001 English Theoretical work and general circulation model (GCM) experiments suggest that the midlatitude jet stream's interaction with large‐scale topography can drive intraseasonal oscillations in large‐scale atmospheric circulation patterns. In support of this theory, we present new observational evidence that mountain‐induced torques play a key role in 15–30‐day oscillations of the Northern Hemisphere circulation's dominant patterns. The affected patterns include the Arctic Oscillation (AO) and the Pacific‐North‐American (PNA) pattern. Positive torques both accelerate and anticipate the midlatitude westerly winds at these periodicities. Moreover, torque anomalies anticipate the onsets of weather regimes over the Pacific, as well as the break‐ups of hemispheric‐scale regimes. Atmospheric sciences 28 7 1207 1210 2001-04-01 http://dx.doi.org/10.1029/2000GL011829 http://hdl.handle.net/10022/AC:P:14372 NNC NNC 2012-08-14 13:38:39 -0400 2012-08-14 13:49:41 -0400 8392 eng