2002 Annual

Thursday, 17 January 2002: 8:30 AM
Frequency analysis of intraseasonal variations in the North American Monsoon System
Eileen A. Hall-McKim, CIRES/Univ. of Colorado, Boulder, CO; and A. Nolin, F. Lo, M. Serreze, and M. Clark
Poster PDF (57.8 kB)
The North American Monsoon System regime experiences climate variations on timescales ranging from intraseasonal to decadal. The challenge facing the climate community is to develop and implement a capability to forecast these variations.

This study investigates the hypothesis that the evolution of the North American Monsoon System (NAMS) is modulated by intraseasonal variations in atmospheric circulation. The monsoon phenomenon undergoes considerable intraseasonal variability with alternating periods of widespread, heavy thunderstorm activity (bursts) and drier periods (breaks). Intraseasonal fluctuations of observed summer precipitation for Arizona and New Mexico are analyzed to ascertain their spatial/temporal coherence.

Spectral characteristics of intraseasonal burst/break activity within (NAMS) are examined using a 41-year dataset of July-August average daily precipitation for Arizona and New Mexico. Wavelet analysis is used to explore both the dominant modes of variability and how those modes vary in time.

Our preliminary analysis of burst/break activity associated with this monsoon system displays the existence of a 10-20 day periodicity. The existence of a relationship between summer monsoon activity and a 10-20 mode has been indicated for the Indian summer monsoon (Krishnamurti and Bhalme, 1976; Krishnamurti and Ardunay, 1980).

This work represents a step in a broader investigation that will examine interactions between the land surface and atmospheric circulation as they relate to the North American Monsoon System. Further analysis will examine comparison to indices of large- scale atmospheric features i.e., ENSO, PNA, and MJO, and possible land surface forcing of anomalous snow extent over North America.

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