21st Conference on Climate Variability and Change


Interannual variability of the west coast cyclone landfall and its influence on the western U.S. winter precipitation

Yi Deng, Georgia Institute of Technology, Atlanta, GA; and B. Myoung

This study examines the impact of cyclone landfall activity on the characteristics of both winter-mean and extreme precipitation in the western U.S. A cyclone landfall function (CLF) was derived from a dataset of objectively-identified cyclone tracks in 27 winters (1979/80-2005/06). The leading Empirical Orthogonal Function (EOF1) of the CLF was found to be responsible for the EOF1 of the winter precipitation in the western U.S., which is a monopole mode centered over the Pacific Northwest and northern California. On the other hand, the EOF2 and EOF3 of the CLF, clearly being modulated by the ENSO signal at the interannual scale, contribute significantly to the EOF2 of the winter precipitation, which indicates that above-normal precipitation in the Pacific Northwest and its immediate inland regions tends to be accompanied by below-normal precipitation in California and the southwest U.S. and vice versa. A composite analysis further reveals that cyclone landfall affects the winter-mean precipitation by inducing changes in both the number of rainy days per winter and the extremeness of precipitation quantified in terms of the 95th percentile of the daily rain rate and the probability of precipitation being heavy given a rainy day. The implications of the leading CLF modes for the water resources and the occurrence of extreme hydrological events in the western U.S., as well as their dynamical linkage to the Pacific storm track will also be discussed.

Session 12A, Seasonal-interannual variability II
Thursday, 15 January 2009, 8:45 AM-9:45 AM, Room 129A

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