Climate variability in the southwestern United States as reconstructed from tree-ring chronologies

The primary goal of this research is to gain a better understanding of the spatial and temporal relationships between atmospheric circulation features and winter climate variability in the southwestern United States, and to investigate the variations in these relationships over the past three centuries. A set of six circulation indices is compiled that describes circulation features important to winter climate variability in this region. This set includes pre-existing indices such as the SOI and a modified PNA index, as well as regionally-tailored indices. A network of 88 tree-ring chronologies is then used to reconstruct the indices and the regional winter climate variables: numbers of rainy days (a variable not previously reconstructed with tree rings) and mean maximum temperature. Analyses suggest that three types of circulation features have influenced winter climate in the Southwest over the past three centuries. Although ENSO-related circulation patterns have been an important factor, especially in the 20th century, circulation patterns featuring a southwestern low appear to be as important if not more important to climate in some time periods. Results suggest that low frequency variations in atmospheric circulation patterns have occurred over the past three centuries and have had spatially and temporally varying impacts on winter climate in the Southwest.