Harmonic analysis of monthly insolation levels in the United States

The purpose of this paper is to analyze independent temporal variance structures in long-term mean monthly insolation data for the conterminous United States. Harmonic analysis is applied to the annual march of insolation levels at 221 stations, and nearly all variance in the data is explained by one harmonic fit. The statistics from the harmonic analysis display coherent spatial patterns that reveal the extent to which radiation levels are affected by synoptic climatological phenomena. The results suggest a method for accurately interpolating insolation estimates using as few as three parameters.