Spectral properties of tree-ring data in the United States southwest as related to El Nino/Southern Oscillation

The spatial extent and geographic orientation of significant interregional tree-ring correlation in the ENSO band is similar to that in the entire 0 to π frequency range. Spatial correlations with the Southwest region are highly significant (99.9% level) and in-phase in a band oriented southwest-northeast from Southern California to Colorado, and weakly significant (95% level) and in-phase with northwestern Wyoming. Spatial correlation of Southwest tree rings with other regional tree-ring series is strongest outside the ENSO band, at wavelengths 20 yr and longer. An important component of low-frequency variance in Southwest trees is a pronounced downward growth trend from the early 1900s to the 1950s. -from Author