| Summary: | NCEP reanalyses have been used to compute the climatological isentropic potential vorticity (IPV) budget at the 315K level for 39 winters and for those winters with a North Atlantic Oscillation (NAO) as well as winters with a Pacific/North American (PNA) pattern. The climatology shows two main IPV sources, each being upstream of the two main centers of positive PV on the east coasts of North America and Asia. The results for the winters with a NAO (PNA) anomaly show, in particular, that the mean-winter IPV anomalies associated with these patterns also have upstream sources. The importance of the latter is not as clear as that of the continential sources that maintain the climatological centers. The mean-winter IPV advection that balances the IPV sources/sinks is composed of the advection by the time-mean flow and by the transient eddies (decomposed into high- and low-frequency components), where the former is the dominant component. The latter are found to produce a negative feedback in that they act to reduce the amplitude of the IPV anomaly. For the NAO anomaly, low-frequency transient advection is more important, while high-frequency transient advection is more statistically significant for the PNA anomaly. Both the high and low-frequency advection have comparable contributions in maintaining the climatological distribution of the stationary eddy IPV.
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