The Surface Cloud Grid value-added product (SFCCLDGRID VAP) uses output from the Radiative Flux Analysis VAP at the Southern Great Plains (SGP) central and extended facilities. It applies a multi-pass weighted sum analytic approximation technique (Caracena 1987), which uses Gaussian weighting and an imposed scale length, to interpolate to a 0.25-by-0.25-degree latitude-longitude grid over the SGP domain. The output, like the input, includes only solar elevation angles of 10 degrees or greater.
SFCCLDGRID produces gridded output for cloud fraction, the ratio of measured over clear-sky shortwave total (both unshaded pyranometer and sum of direct + diffuse) and direct irradiance, the estimated clear-sky fit total shortwave irradiance, and the estimated clear-sky fit direct shortwave irradiance. The ratio measured over clear-sky direct shortwave, in conjunction with the total shortwave ratio and clear-sky total and direct irradiance, allows for component evaluation of the irradiance and cloud effects. These output variables were chosen because the intent is to use the SFCCLDGRID VAP output for model comparisons, as well as climatological and statistical research.