Tree-ring reconstructions of circulation indices

Generalized circulation indices, as descriptors of atmospheric circulation features, have been used to analyze the relationships between circulation and regional climates. Currently, data for such circulation indices are limited. Records for some indices extend back into the 19th century, but most are based on data that exist for less than 100 yr. Tree rings have been successfully used to extend records of circulation indices, most notably the Southern Oscillation Index. Researchers are continuing to improve reconstructions and to explore the potential of reconstructing other indices. In contrast to more general indices, it is possible to select and/or construct indices that describe circulation features important to a specific region. These regionally tailored circulation indices, along with more general indices that describe features also influencing the climate of a region, can be reconstructed from tree rings. Reconstructions can provide information about variability in atmospheric circulation and about the interactions between influential circulation features in past centuries. In this paper, an example of such a study is given in which a set of circulation indices, compiled for the southwestern U.S., is reconstructed from tree rings. This preliminary study demonstrates the potential value of regionally tailored circulation indices and the reconstruction of these circulation indices for gaining an understanding of how circulation patterns may influence regional climates, on scales of decades to centuries.