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Evolution of Subduction Planetary Waves with Application to North Pacific Decadal Thermocline Variability

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  • 1 Department of Atmospheric and Oceanic Sciences and Center for Climatic Research, University of Wisconsin—Madison, Madison, Wisconsin
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Abstract

The evolution of decadal subduction temperature anomalies in the subtropical North Pacific is studied using a simple and a complex ocean model. It is found that the amplitude of the temperature anomaly decays faster than a passive tracer by about 30%–50%. The faster decay is caused by the divergence of group velocity of the subduction planetary wave, which is contributed to, significantly, by the divergent Sverdrup flow in the subtropical gyre. The temperature anomaly also seems to propagate southward slower than the passive tracer, or mean ventilation flow. This occurs because the mean potential vorticity gradient in the ventilated zone is directed eastward; the associated general beta effect produces a northward propagation for the temperature anomaly, partially canceling the southward advection by the ventilation flow.

Corresponding author address: Z. Liu, Center for Climatic Research, University of Wisconsin—Madison, 1225 W. Dayton St., Madison, WI 53706-1695. Email: zliu3@facstaff.wisc.edu

Abstract

The evolution of decadal subduction temperature anomalies in the subtropical North Pacific is studied using a simple and a complex ocean model. It is found that the amplitude of the temperature anomaly decays faster than a passive tracer by about 30%–50%. The faster decay is caused by the divergence of group velocity of the subduction planetary wave, which is contributed to, significantly, by the divergent Sverdrup flow in the subtropical gyre. The temperature anomaly also seems to propagate southward slower than the passive tracer, or mean ventilation flow. This occurs because the mean potential vorticity gradient in the ventilated zone is directed eastward; the associated general beta effect produces a northward propagation for the temperature anomaly, partially canceling the southward advection by the ventilation flow.

Corresponding author address: Z. Liu, Center for Climatic Research, University of Wisconsin—Madison, 1225 W. Dayton St., Madison, WI 53706-1695. Email: zliu3@facstaff.wisc.edu

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