Interannual to interdecadal variations of the regionalized surface climateof the United States and relationships to generalized flow parameters

This analysis attempts to discern primary causes of interannual and interde cadal climate variations for precipitation and temperature regions of the c onterminous United States. Varimax rotated principal components analysis of annual climate division data is used in the derivation of nine precipitati on and five temperature regions. Each region's time series is examined for underlying linear trends, representing long-term climate change, and tests for variance changes, to determine regional climate variability shifts. The first six precipitation components, representing the entire eastern half o f the country and the Northwest, displayed significant temporal increases. Of these, four displayed significant increases in interannual variability t hrough time. For temperature, only the Southwestern region showed a signifi cant change (increase) through time. However, significant reductions in tem perature variability were confirmed for three regions. To determine the cau ses of the derived climate shifts, correlation analysis was performed with various atmospheric teleconnection indices. Precipitation trends are most s trongly associated with variations in the Southern Oscillation Index (SOI) at the interannual time scale while interdecadal variations are associated more with variations in the Pacific/North American (PNA) teleconnection. Bo th interannual and interdecadal variations of regional temperature are most strongly related to the PNA, except for the Southwest, which showed a sign ificant correlation to the SOI. This suggests that El Nino/Southern Oscilla tion (ENSO) events are the source for much of the precipitation change evid ent in the eastern and Northwestern United States and temperature change in the Southwest.