Both data sets are based on actual recordings from official weather stations around the world going back up to 25 years and archived as the Integrated Surface Hourly Database (ISD) by the (US) National Center for Environmental Information (NCEI). Extensive processing equivalent in scope to the TMY3 files has resulted in complete weather files with solar radiation, daylight illuminance, and precipitation, in addition to the standard parameters of temperature, humidity, pressure, wind speed and direction, etc. For more details, please go to:
http://weather.whiteboxtechnologies.com.