INTERANNUAL VARIABILITY IN WESTERN US PRECIPITATION

Low-frequency (interannual or longer period) climatic variability is o f interest, because of its significance for the understanding and pred iction of protracted climatic anomalies. Since precipitation is one of the key variables driving various hydrologic processes, it is useful to examine precipitation records to better understand long-term climat e dynamics. Here, we use the multi-taper method of spectral analysis t o analyze the monthly precipitation time series (both occurrence and a mount) at a few stations along a meridional transect from Priest River , ID to Tucson, AZ. We also examine spectral coherence between monthly precipitation and widely used atmospheric indices, such as the centra l Northern Pacific (CNP) and southern oscillation index (SOI). This an alysis reveals statistically significant 'signals' in the time series in the 5-7 and 2-3 year bands. These interannual signals are consisten t with those related to El-Nino southern oscillation (ENSO) and quasi- biennial variability identified by others. (C) 1998 Elsevier Science B .V. All rights reserved.