Development of a semi-parametric PAR partitioning model for the contiguous US

Abstract

15 A semi-parametric PAR diffuse radiation model was developed using commonly measured 16 climatic variables from 114 site-years of data from 19 AmeriFlux sites. The model has a 17 logistic form and improves upon previous efforts, using a larger data set and physically viable 18 climate variables as predictors, including relative humidity, clearness index, surface albedo, 19 and solar elevation angle. Model performance was evaluated by comparison with a simple 20 cubic polynomial model developed for the PAR spectral range. The logistic model 21 outperformed the polynomial model with an improved coefficient of determination and slope 22 relative to measured data (logistic: R 2 = 0.76; slope=0.76; cubic: R 2 = 0.72; slope=0.73), 23 making this the most robust PAR-partitioning model for the US subcontinent currently 24 available. 25