Inter-regional correlation in tree-growth variations in the western United States, 1513-1964, at ENSO, sunspot, and longer frequency bands

Cross-spectral analysis of regional tree-ring data suggests the spatial pattern of correlation between moisture variations in the Sierra Nevada of central California and in other parts of the western United States is frequency dependent. Short wavelengths (2.8 to 10.7 years), perhaps associated with El Niño/Southern Oscillation, are strongly coherent both to the north (Oregon) and to the south (Southern California). Longer wavelengths (45 to 75 years) are strongly coherent only to the north. Frequency bands corresponding to annual sunspot series were associated with relatively weak patterns of spatial correlation.