Interdependence of radiation and microphysics in cirrus clouds.

The important microphysical relationships determining the radiative properties and growth of ice crystals in stratiform cirrus clouds are investigated. A horizontally infinite cloud layer is modeled in the midlatitude upper troposphere. Classical expressions for ice particle growth and sublimation are coupled to those for radiative energy exchange in order to follow ice particle evolution within the cloud. We have followed the one-dimensional temporal evolution of 1-km thick cirrus cloud layers subsiding in still air. Crystals at cloud top grow larger with time while those at cloud base sublimate as the cloud settles into dry air, with the vertical fall distance greater for larger initial crystal lengths. The temporal evolution of the cloud microphysical characteristics results in modification of the radiation fields, both within the cloud and at the cloud boundaries.-from Authors