Evaluation of the Hydrometeor Layers in the East and West Pacific within ISCCP Cloud-Top Pressure–Optical Depth Bins Using Merged CloudSat and CALIPSO Data

Abstract

The International Satellite Cloud Climatology Project (ISCCP) provides a multidecadal and global description of cloud properties that are often grouped into joint histograms of column visible optical depth τ and effective cloud-top pressure Ptop. It has not been possible until recently to know the actual distributions of hydrometeor layers within the ISCCP Ptop–τ bins. Distributions of hydrometeor layers within the ISCCP Ptop–τ conditional probability space using measurements from the CloudSat Cloud Profiling Radar and the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) lidar within two 40° × 40° regions in the eastern and western equatorial Pacific over a 2-yr period are examined. With the exception of thin cirrus and stratocumulus, the authors show that of the Ptop–τ types that are commonly analyzed, none of the types contain unique distributions of geometrically defined layer types but tend to be populated by diverse sets of hydrometeor layers whose bulk profile properties conspire to render specific radiative signatures when interpreted by two-channel visible and IR sensors from space. In comparing the geometric distribution of cloud layers for common Ptop–τ types, it is found that the ISCCP Cirrostratus, Deep Convection, and Stratocumulus types appear to have been drawn from a common geometric distribution of hydrometeor layers. The other six common ISCCP Ptop–τ types do not share this feature. The authors can confidently reject an assumption that even though they have common top-of-atmosphere radiative signatures, they do not appear to share a common distribution of cloud layers and therefore are likely to have significantly different radiative heating profiles and different surface radiative forcing even though their top-of-atmosphere radiative signatures are similar.