Dataset of the regional reanalysis COSMO-REA6. rlds (Surface Downwelling Longwave Radiation in modeling realm(s) atmos): The surface called surface means the lower boundary of the atmosphere. longwave means longwave radiation. Downwelling radiation is radiation from above. It does not mean net downward. When thought of as being incident on a surface, a radiative flux is sometimes called irradiance. In addition, it is identical with the quantity measured by a cosine-collector light-meter and sometimes called vector irradiance. In accordance with common usage in geophysical disciplines, flux implies per unit area, called flux density in physics. COSMO model original name(s): ATHD_S