Solar radiation for National Hydrography Dataset, version 2 catchments in the southeastern United States, 1950 - 2010 at 12-digit hydrologic unit code (HUC12) pour points

This study is based on contiguous direct normal irradiance information from the National Renewable Energy Laboratory. Specifically, these data represent both 12-month specific average and annual average daily total solar resource averaged over surface cells of 0.1 degrees in both latitude and longitude. Spacing is about 10 kilometers in size. Direct normal irradiance is the amount of solar radiation received per unit area. For more information on direct normal irradiance see Introduction to Micrometeorology (Arya, 2001) or Fundamentals of Atmospheric Physics (Salby, 1996). Following the metadata description by the National Renewable Energy Laboratory, these modeled data are based on hourly radiance images from geostationary weather satellites; daily snow cover data; and monthly averages of atmospheric water vapor, trace gases, and the amount of aerosols in the atmosphere to calculate the hourly total insolation (sun and sky) falling on a horizontal surface. Atmospheric water vapor, trace gases, and aerosols were derived from a variety of sources. It is important to note that, where possible, existing ground measurement stations were used by the National Renewable Energy Laboratory to validate the data. Modeled values are suggested to be accurate to approximately 15 percent of a true measured value within the grid cell. For this study, a simple overlay of the location of a streamgage onto the gridded solar radiation data was made to assign January through December direct normal irradiance values, and average annual values at each streamgage. No polygon representing whole or part of the watershed of the streamgage was intersected with the gridded solar radiation data.