Mountain torques and atmospheric oscillations
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.