Peng, S., and J. S. Whitaker, 1998: Mechanisms determining the atmospheric
response to mid-latitude SST anomalies.
J.
Clim. 12, 1393-1408.
(PDF)
ABSTRACT
Mechanisms determining the atmospheric response to mid-latitude SST anomalies
Shiling Peng and Jeffrey S. Whitaker
CIRES, University of Colorado, Boulder, CO
Abstract
Previous GCM experiments demonstrated that a model atmosphere
produces two different responses to a midlatitude warm SST anomaly
over the Pacific under perpetual January and February conditions. To
elucidate the mechanisms responsible for the different GCM responses
and their dependence on the background flow, experiments with two
idealized models are conducted. Experiments with a linear baroclinic
model reveal that the GCM responses at equilibrium are primarily
maintained by the anomalous eddy forcing. The anomalous flow induced
directly by an idealized initial heat source exhibits little sensitivity to the
background flow. Eddy feedbacks on the heating-induced anomalous
flow are examined using a linear storm track model. The anomalous
eddy forcing produced by the storm track model is sensitive to the basic
state. The eddy forcing in January acts to shift the heating-induced
upper-level ridge toward the northeast of the Gulf of Alaska, while in
February it acts to reinforce the ridge. This suggests that the differences
in the GCM responses are primarily associated with differences in the
response of synoptic eddies to the presence of an anomalous ridge at the
end of the Pacific storm track.
The idealized model experiments are also performed with the
observed winter mean flow. The eddy feedbacks depend on the position
of the heating relative to the storm track. With the heating centered over
the western Pacific the eddy-driven anomalous flow reinforces the ridge
over the Pacific, similar to that in GCM February, but much stronger. No
such reinforcement by the transients is found with the heating shifted over
the eastern Pacific. These results suggest that SST anomalies over the
western Pacific perhaps play a more active role in midlatitude
atmosphere-ocean interactions.