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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.
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