Simulated U.S. Drought Response to Interannual and Decadal Pacific SST Variability

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Idealized atmospheric general circulation model (AGCM) experiments by the U.S. Climate Variability and Predictability Program(CLIVAR)DroughtWorkingGroupwere used in order to study the influence of natural modes of sea surface temperature (SST) variability in the Pacific on drought in the contiguous United States. The current study expands on previous results by examining the atmospheric response of threeAGCMs to three different patterns of the idealized Pacific SST anomalies that operate on different time scales: low-frequency (decadal), high-frequency (interannual), and a pan-Pacific pattern that retains characteristics of interannual and decadal variability.While forcing patterns are generally similar in appearance, results indicate that differences in the relative amplitude of the equatorial and extratropical components of the SST forcing are sufficient to give rise to differing teleconnections, leading to regional differences in the amplitude and significance of the precipitation response. Results indicate that the differences in simulated drought response between AGCMs to different cool-phase (La Niña–like) SST patterns are determined bymodel sensitivity to changes in the relative amplitude of the equatorial and extratropical components of the SSTA forcing, the strength of the land– atmosphere coupling, and by the amplitude of internal atmospheric variability. Results indicate that the northwesternUnited States andGreat Plains regions are particularly sensitive to the extratropical component of the SSTforcing.Evidence is also found thatwhen the cool-phase patterns of SST combine, as they have in recent years, constructive interference leads to an enhanced drought response over the Great Plains.