Shortwave Radiation is a radiant energy produced by the sun with wavelengths ranging from infrared through visible to ultraviolet. Shortwave radiation is therefore exclusively associated with daylight hours for a particular location on the Earth's surface. The energy arrives at the top of the Earth's atmosphere with a flux (Watts per square meter) that varies very little during the year and between years. Consequently, the flux is usually taken as a constant for hydrologic simulation purposes. Some of the incoming radiation is reflected by the top of the atmosphere and some is reflected by clouds. A portion of the incoming radiation is absorbed by the atmosphere and some is absorbed by clouds. The Albedo is the fraction of the shortwave radiation arriving at the land surface that is reflected back into the atmosphere. The shortwave radiation that is not reflected or absorbed above the land surface, and is not reflected by the land surface, is available to drive hydrologic processes such as evapotranspiration and snowpack melting.