DeFlorio, M. J., D. W. Pierce, D. R. Cayan and A. J. Miller, 2013:
extreme precipitation events and their
relation to ENSO and PDO in CCSM4
Journal of Climate, 26, 4231-4243.
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 Niñouthern
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.