On some characteristic variations in warm season precipitation over the central United States (1910-2000)

Abstract

On the basis of an observational data set that spans most of the twentieth century, we show that warm season precipitation over the central United States aligns into six large-scale regions. Using two different measures of seasonal precipitation, frequency and intensity, we explore the basic question: To what extent are the observed interannual variations in regional precipitation associated with fluctuations in both large-scale climate modes, the El Niño/Southern Oscillation (ENSO) phenomena and the Pacific Decadal Oscillation (PDO), and more local-scale antecedent moisture conditions? The principal study findings are that the teleconnection between ENSO and regional rainfall is best developed during the early part of the warm season in association with El Niño events, but that modest spatial shifts in the teleconnection occur depending upon phase of the PDO. The investigation reveals little evidence for a teleconnection between ENSO and regional rainfall during La Niña events. Moreover, late in the season, ENSO teleconnectivity is confined largely to the northern part of the study area. While the influence of large-scale climate modes apparently diminishes late in the warm season, this study provides additional empirical evidence to connect early season moisture demand with subsequent rainfall regimes. Copyright 2002 by the American Geophysical Union.