P3.6
Spatial coherence of Southwest U. S. rainfall on intraseasonal and interannual timescales
Eileen A. Hall-McKim, University of Colorado, Boulder, CO; and G. N. Kiladis
The southwestern U. S. is particularly sensitive to variability in climate, and management of water resources in this arid region of growing population presents a formidable challenge. Improved knowledge of hydroclimatic variability is a first step in better planning and management of systems which are both directly and indirectly climate dependent.
Precipitation is produced by a complex combination of interacting processes operating over a wide range of space and timescales. Southwestern U.S. precipitation regimes experience climate variability on a wide range of potentially interacting timescales ranging from intraseasonal to decadal. It is therefore important to identify and isolate various mechanisms responsible for these fluctuations in space and time. Some possible forcings are introduced by natural modes of atmospheric circulation associated with large-scale processes such as ENSO and MJO, along with changes in intraseasonal wave activity emanating out the North Pacific. The challenge facing the climate community is to develop and implement a capacity to forecast these variations.
In this contribution, we examine spatial coherence of Southwest U.S. rainfall patterns, utilizing wavelet analysis (WT) and empirical orthogonal function (EOF) analysis to describe the space-time behavior of Southwest U. S. rainfall and adjacent Mexico. WT applied to time-series allows not only detection of the periodic fluctuation in frequency space, but also their temporal localization. Hence, the combination of WT Analysis with EOF allows us to examine these characteristics over one region.
We analyze daily precipitation data from station and reanalysis data for the years 1958-2002 in order to identify dominant modes of variability of precipitation and coherence with large scale circulation. Preliminary analyses reveal that summer rainfall in the southwestern U. S. is modulated by large-scale, low-frequency (20-50 day) dynamics. Improved understanding of these interactions could lead to more accurate seasonal to subseasonal forecasting of precipitation.
Poster Session 3, ENSO and Monsoons (Hall 4AB)
Thursday, 15 January 2004, 9:45 AM-11:00 AM, Hall 4AB
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