Midwinter suppression and interannual variability of the Pacific storm
track: Examples of eddy-mean flow coupling?
The storm track and mean flow patterns associated with the midwinter suppression and interannual variability of the Pacific storm track are identified using NCEP Reanalysis data from 1979 to present. Cross spectrum analysis is used to investigate whether these patterns exist on subseasonal timescales in midwinter, and to determine the lead-lag relationship between storm track and mean flow anomalies on subseasonal timescales. The PNA-like mean flow pattern associated with interannual variability appears to dominate variability at a period of 60 days, but not 20 days, while the midwinter suppression mean flow pattern does not appear important at any subseasonal timescale. The interannual storm track pattern appears to lead the interannual PNA-like mean flow pattern by 2-4 days at a period of 20 days, while the patterns are approximately simultaneous at a period of 60 days. It is suggested that the patterns of interannual variability are more likely to be an example of coupled eddy-mean flow variability, while midwinter suppression is primarily externally forced. The tropical precipitation patterns associated with midwinter suppression and interannual variability are shown to motivate future work on the forcing of the midlatitude storm track-mean flow system by tropical convection.
7 May, 2003
2 PM/ DSRC 1D 403
(Coffee at 1:50 PM)