Both midwinter suppression and interannual variability of the Pacific storm track are associated with mean flow patterns that could plausibly reinforce and be reinforced by the corresponding storm track anomalies. The hypothesis that both are examples of eddy-mean flow coupling is investigated from the point of view that similar relationships between the storm track and mean flow anomalies should exist on subseasonal time scales if they are coupled.

Cross spectrum analysis indicates that the storm track and mean flow patterns associated with interannual variability are coherent and nearly simultaneous at periods greater than 30 days, while the storm track pattern leads the mean flow pattern at periods between 15 and 30 days. This suggests that the interannual variability of the Pacific storm track results from eddy-mean flow coupling on time scales greater than 30 days, where random variations in the storm track have been sufficiently averaged for the mean flow to organize the storm track. However, there is little coherence between the storm track and mean flow patterns associated with midwinter suppression at subseasonal time scales. Midwinter suppression of the Pacific storm track appears to be externally forced, perhaps by the shift of tropical convection into the Southern Hemisphere.