Harmonic Analysis of the Seasonal Cycle in Precipitation over the United States: A Comparison between Observations and a General Circulation Model

Abstract

Using precipitation values obtained from a version of the Oregon State University general circulation model and observational gridded data, harmonic analysis has been employed to study the seasonal variation of precipitation over the conterminous United States. Maps of the first, second and third harmonic amplitudes and phases provide a useful source of comparison between model output and observational data. Results indicate that the method of harmonic analysis allows a more analytical comparison between model predictions and data than the conventional approach of representing the annual march in the form of a curve of mean monthly rainfall amounts. The method delineates regional boundaries of the various precipitation regimes in the United States. The GCM captures a significant amount of the regional detail in precipitation climatology when its results are decomposed by harmonic analysis.