Benchmarking radiation transfer models in clouds

Kurzfassung

Radiative transfer in the atmosphere is the backbone of any atmospheric property retrieval. The determination of clouds, aerosols, trace gases or surface properties from space observations is based on an accurate forward modeling of radiation. The "Intercomparison of 3D Radiation Codes" (I3RC, http://i3rc.gsfc.nasa.gov/) has been initiated in the late 1990s. It is an ongoing project aimed at the comparison and improvement of three-dimensional radiative transfer models - a highly sophisticated class of models which allow to quantitatively calculate radiative transfer through highly inhomogeneous atmospheres, in particular clouds. Although these codes at present cannot be used in an operational sense - due to their high computational demands and the often limited resolution of satellite sensors - they allow the simulation of benchmark cases which may serve as a framework to test operational retrievals. The talk will explain the relevance of three-dimensional radiative transfer and show how the I3RC can help to quality control satellite products and algorithms. The first two phases of the I3RC, finished in 1999 and 2000, showed that state-of-the-art 3D codes may agree at the 1% level for a set of well-defined cases. The third phase - to be started in 2006 - will include a highly realistic case based on a combination of different satellite observations.