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GEOPHYSICAL RESEARCH LETTERS, VOL. 28, NO. 7, PAGES 1207–1210, 2001

Mountain Torques and Atmospheric Oscillations

François Lott

Laboratoire de Météorologie Dynamique, Université Pierre et Marie Curie, Paris, France

Andrew W. Robertson

Department of Atmospheric Sciences and IGPP, University of California at Los Angeles, USA

Michael Ghil

Department of Atmospheric Sciences and IGPP, University of California at Los Angeles, USA

Abstract

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.

Received 26 May 2000; accepted 20 November 2000.

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Citation: Lott, F., A. W. Robertson, and M. Ghil (2001), Mountain Torques and Atmospheric Oscillations, Geophys. Res. Lett., 28(7), 1207–1210.

Copyright 2001 by the American Geophysical Union.