Table 1-1. Solar Radiation and Meteorological Elements in the NSRDB
Global horizontal radiation in Wh/m2Atmospheric pressure in millibars
Direct normal radiation in Wh/m2Wind direction in increments of 10 degrees
Diffuse horizontal radiation in Wh/m2Wind speed in m/s
Extraterrestrial radiation (ETR) in Wh/m2Horizontal visibility in km
Direct normal ETR in Wh/m2Ceiling height in decameters
Total sky cover in tenthsPresent weather
Opaque sky cover in tenthsTotal precipitable water in mm
Dry-bulb temperature in oCAerosol optical depth
Dew-point temperature in oCSnow depth in cm
Relative humidity in percentNumber of days since last snowfall


http://www.nrel.gov/rredc