Cloud microphysics retrieval in highly three-dimensional situations

Abstract

The CLAIM-3D (cloud aerosol interaction mission in 3-D) passive cloud side viewing sensor concept is planned to become a new means of measuring the vertical profile of cloud microphysical properties, e.g., from airborne perspective or eventually from a satellite platform. Inherent to the complex viewing and illumination geometry and the fact that such a profile has to be derived on high spatial resolution is the need for the consideration of 3D radiative transport. Based on a large number of realistic deep convection cloud scenes from a 3D cloud resolving model (Goddard Cumulus Ensemble model) a data base of related observable radiances is generated, using a 3D Monte Carlo radiative transfer model (MYSTIC). Presented are the technical optimizations and the necessary trade-offs between Monte Carlo model accuracy and computational speed in order to facilitate the generation of a large data base of simulated observations in channels in the visible, NIR and IR spectral range. This data set is then used to explore the limitations of a conventional plane-parallel approach to the cloud side remote sensing of profiles of cloud phase and effective particle size. Furthermore it is demonstrated how the data base can as well serve as the basis for a Bayesian retrieval algorithm of the same properties which is accounting for the uncertainty due to 3D radiative effects and the variability of the cloud particle population