A semi-parametric PAR diffuse radiation model
was developed using commonly measured climatic variables
from 108 site-years of data from 17 AmeriFlux sites. The
model has a logistic form and improves upon previous efforts
using a larger data set and physically viable climate
variables as predictors, including relative humidity, clearness
index, surface albedo and solar elevation angle. Model performance
was evaluated by comparison with a simple cubic
polynomial model developed for the PAR spectral range.
The logistic model outperformed the polynomial model with
an improved coefficient of determination and slope relative
to measured data (logistic: R² = 0.76; slope = 0.76; cubic:
R² = 0.73; slope = 0.72), making this the most robust PAR-partitioning
model for the United States currently available.This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by Copernicus Publications on behalf of the European Geosciences Union. The published article can be found at: http://www.geoscientific-model-development.net/home.html
