Low-level maritime water clouds play a critical role in both global and regional climate, through their strong radiative effects interactions with aerosols and precipitation. Among others, the cloud particle effective radius (re) is perhaps the most important cloud microphysical parameter. It not only has a significant influence on cloud radiative forcing responses to aerosol modification, but is also a key proxy useful for understanding aerosol-cloud-precipitation interactions. The importance of re has motivated the development of various satellite-based remote-sensing techniques for monitoring the global cloud re from space.
In this talk, I will begin with an overview of the climatic effects and the microphysical structure of marine boundary layer clouds. Then, I briefly introduce two popular satellite-based re remote sensing algorithms, one based on MODIS radiometric and the other on POLDER polarization measurements. The major part of this talk will be concentrated on open issues in re retrievals related to 3-D cloud structure. In particular, I will present our recent study on the difference between re retrievals from MODIS 2.1µm band and 3.7µm band. I will also introduce a modeling framework, based on the combination of LES model and 3-D radiative transfer model (I3RC), that we recently developed for investigating open issues in MODIS cloud property retrieval. Finally, I will briefly talk about implications of our study for climate studies.