Decadal variations in the strength of ENSO teleconnections with precipitation in the western United States

Changing patterns of correlations between the historical average June-Novem ber Southern Oscillation Index (SOI) and October-March precipitation totals for 84 climate divisions in the western US indicate a large amount of vari ability in SOI/precipitation relations on decadal time scales. Correlations of western US precipitation with SOI and other indices of tropical El Nino -Southern Oscillation (ENSO) processes were much weaker from 1920 to 1950 t han during recent decades. This variability in teleconnections is associate d with the character of tropical air-sea interactions as indexed by the num ber of out-of-phase SOI/tropical sea surface temperature (SST) episodes, an d with decadal variability in the North Pacific Ocean as indexed by the Pac ific Decadal Oscillation (PDO). ENSO teleconnections with precipitation in the western US are strong when SOI and NINO3 are out-of-phase and PDO is ne gative. ENSO teleconnections are weak when SOI and NINO3 are weakly correla ted and PDO is positive. Decadal modes of tropical and North Pacific Ocean climate variability are important indicators of periods when ENSO indices, like SOI, can be used as reliable predictors of winter precipitation in the US. Copyright (C) 1999 Royal Meteorological Society.