DeFlorio, M. J., D. W. Pierce, D. R. Cayan and A. J. Miller, 2013:

Western U.S. extreme precipitation events and their relation to ENSO and PDO in CCSM4

Journal of Climate, 26, 4231-4243.

Abstract. Water resources and management over the Western U.S. are heavily impacted by both local climate variability and the teleconnected responses of precipitation to the El NiƱouthern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO). In this work, regional precipitation patterns over the western U.S. and linkages to ENSO and PDO are analyzed using output from a CCSM4 pre-industrial control run and observations, with emphasis on extreme precipitation events. CCSM4 produces realistic zonal gradients in precipitation intensity and duration over the western U.S., with higher values on the windward side of the Cascade and Sierra Mountains and lower values on the leeward. Compared to its predecessor CCSM3, CCSM4 shows an improved teleconnected signal of both ENSO and the PDO to large scale circulation patterns over the Pacific/North America region and also to the spatial pattern and other aspects of western U.S. precipitation. The so-called .drizzle. problem persists in CCSM4 but is significantly improved compared to CCSM3. In particular, it is found that CCSM4 has substantially less precipitation duration bias than is present in CCSM3. Both the overall and extreme intensity of wintertime precipitation over the western U.S. show statistically significant linkages with ENSO and PDO in CCSM4. This analysis provides a basis for future studies using GHG-forced CCSM4 runs.

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