Extended Abstract (200K)2.4
Persistent positive anomalies in the Southern Hemisphere circulation
James A. Renwick, National Institute of Water and Atmospheric Research, Wellington, New Zealand
The climatology of persistent positive anomalies (PPAs, or "blocking") has been documented for the Southern Hemisphere by a number of authors over the last two decades. The New Zealand region has often been identified as one of the main locations for blocking activity. However, recent work suggests that the southeast Pacific, west of southern Chile, is the main Southern Hemisphere blocking region.
This presentation discusses a long-term climatology of Southern Hemisphere blocking, based upon identification of PPAs in daily 500hPa fields from the NCEP/NCAR reanalyses. It demonstrates that while the New Zealand region does experience relatively frequent blocking events, the southeast Pacific has a far higher incidence of blocking cases. Possible reasons for differences between studies of Southern Hemisphere blocking are discussed.
A cluster analysis of monthly PPA statistics shows that southeast Pacific blocking appears to occur in isolation, while blocking events near New Zealand tend to occur as part of a zonal wave number three pattern. The relative importance of tropical forcing upon these two different hemispheric blocking configurations will be discussed.
Session 2, Tropical-Extratropical Interactions and Teleconnections over the Southern Hemisphere I
Monday, 24 March 2003, 10:30 AM-3:00 PM
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