Evolution of subduction planetary waves with application to North Pacific decadal thermocline variability

The evolution of decadal subduction temperature anomalies in the subtropica l 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 pa ssive tracer by about 30%-50%. The faster decay is caused by the divergence of group velocity of the subduction planetary wave, which is contributed t o, significantly, by the divergent Sverdrup flow in the subtropical gyre. T he temperature anomaly also seems to propagate southward slower than the pa ssive tracer, or mean ventilation flow. This occurs because the mean potent ial vorticity gradient in the ventilated zone is directed eastward; the ass ociated general beta effect produces a northward propagation for the temper ature anomaly, partially canceling the southward advection by the ventilati on flow.