The study of Shabbar et al. (1997) relating winter cooling trends in eastern Canada-West Greenland to shifts in the Baffin Island -West Atlantic (BWA) circulation, specifically the Canadian Polar Trough (CPT) identifies a 'new' index of temperature variability in the region. A complementary study of the same area for summer was in fact carried out by Keen (1980). Keen showed that colder (milder) summers are associated with an eastward (westward) displacement of the CPT at 700 and 500 mb. Sea ice clearance in Baffin Bay is also well correlated with summer temperature. Colder summers and an eastward shift of the CPT are also linked to stronger upper westerlies regionally and over most of the hemisphere. Across Canada, meridional temperature grandients and the arctic front are strengthened. Under such regimes there is an increase in cyclone activity north and east of Baffin Island. There was an overall eastward shift of the CPT between 1951 -1960 and 1964 -1973. During 1964-1973, cyclone frequency increased by 35% and positive vorticity flux at 500 mb over Baffin Bay approximately doubled relative to 1951-1960.
The large negative departure of temperature found for winter 1972 was interestingly matched by a pronounced cold summer in 1972 when the sea ice did not fully clear from Baffin Bay. The possibility of seasonal persistence effects is not discussed by Shabbar et al., although Chapman and Walsh (1993, Figure 2) show that there is a cooling trend over Baffin Bay in all four seasons for 1961-1990. Clearly, the year-round circulation characteristics of eastern North America and their role in establishing such a pronounced regional departure from the positive temperature trends over the rest of the subarctic during 1961-1990 merit further study.