Remote sensing of water cloud droplet size distributions using the backscatter glory: a case study

[摘要] Cloud single scattering properties are mainly determined bythe effective radius of the droplet size distribution. There are onlyfew exceptions where the shape of the size distribution affects theoptical properties, in particular the rainbow and the glorydirections of the scattering phase function. Using observations by theCompact Airborne Spectrographic Imager (CASI) in 180° backscattergeometry, we found that high angular resolution aircraft observationsof the glory provide unique new information which is not availablefrom traditional remote sensing techniques: Using only one singlewavelength, 753nm, we were able to determine not only opticalthickness and effective radius, but also the width of the sizedistribution at cloud top. Applying this novel technique tothe ACE-2 CLOUDYCOLUMNexperiment, we found that the size distributions were much narrowerthan usually assumed in radiation calculations which is in agreement within-situ observations during this campaign. While the shape of the sizedistribution has only little relevance for the radiative propertiesof clouds, it is extremely important for understanding their formationand evolution.

[学科分类] 大气科学