Journal of Physical Oceanography: Vol. 29, No. 5,
pp. 1056-1070.
Subduction of Decadal North Pacific Temperature Anomalies:
Observations and Dynamics
Niklas Schneider and Arthur J. Miller
Scripps Institution of Oceanography, La Jolla, California
Michael A. Alexander
CIRES, University of Colorado, Boulder, Colorado
Clara Deser
National Center for Atmospheric Research, Boulder, Colorado
(Manuscript received 9 January 1998, in final form 6 July 1998)
Observations of oceanic temperature in the upper 400 m reveal decadal signals that
propagate in the thermocline along lines of constant potential vorticity from the
ventilation region in the central North Pacific to approximately 18°N in the
western Pacific. The propagation path and speed are well described by the
geostrophic mean circulation and by a model of the ventilated thermocline. The
approximate southward speed of the thermal signal of 7 mm s-1 yields a
transit time of approximately eight years. The thermal anomalies appear to be forced
by perturbations of the mixed layer heat budget in the subduction region of the
central North Pacific east of the date line. A warm pulse was generated in the
central North Pacific by a series of mild winters from 1973 to 1976 and reached
18°N around 1982. After 1978 a succession of colder winters initiated a cold
anomaly in the central North Pacific that propagated along a similar path and with
a similar speed as the warm anomaly, then arrived in the western tropical Pacific at
18°N around 1991. Tropical Ekman pumping, rather than further propagation of the
midlatitude signal, caused the subsequent spread into the equatorial western Pacific
and an increase in amplitude. Historical data show that anomalous sea surface
temperature in the equatorial central Pacific is correlated with tropical Ekman
pumping while the correlation with thermal anomalies in the North Pacific eight
years earlier is not significant. These results indicate no significant coupling in
the Pacific of Northern Hemisphere midlatitudes and the equatorial region via
advection of thermal anomalies along the oceanic thermocline.
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Hongjun Zhang:
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