The use of tree-ring chronologies to show spatial and temporal changes in an air mass boundary

Eleven tree-ring chronologies on either side of a winter air mass boundary in the western United States are examined for evidence of spatial patterning of tree growth consistent with the boundary. Four of the sites are the first published for the Great Salt Lake basin. Principal components analyses group the chronologies into three regions. Analyses of 100-year time periods, overlapped by 50 years, show changes in group membership over time. The Great Salt Lake sites consistently group together into a distinct region. The zonal differentiation of the regions and inferred orientation of the climatic boundary was a feature of the eighteenth and nineteenth centuries. The orientation was more meridional in the twentieth century, as it had been in the seventeenth and early eighteenth centuries.