Retrieval of Ice‐Over‐Water Cloud Microphysical and Optical Properties Using Passive Radiometers.

Current satellite cloud products from passive radiometers provide effective single‐layer cloud properties by assuming a homogeneous cloud in a pixel, resulting in inevitable biases when multiple‐layer clouds are present in a vertical column. We devise a novel method to retrieve cloud vertical properties for ice‐over‐water clouds using passive radiometers. Based on the absorptivity differences of liquid water and ice clouds at four shortwave‐infrared channels (centered at 0.87, 1.61, 2.13, and 2.25 μm), cloud optical thicknesses (COT) and effective radii of both upper‐layer ice and lower‐layer liquid water clouds are inferred simultaneously. The algorithm works most effectively for clouds with ice COT < 7 and liquid water COT > 5. The simulated spectral reflectances based on our retrieved ice‐over‐water clouds become more consistent with observations than those with a single‐layer assumption. This new algorithm will improve our understanding of clouds, and we suggest that these four cloud channels should be all included in future satellite sensors. Plain Language Summary: Over a quarter of clouds in the atmosphere overlap in a vertical column, and ignoring the cloud vertical distribution may significantly influence estimation of their radiative effects. However, information about cloud vertical structures is mostly provided by in situ or active instruments with limited spatiotemporal resolution. Cloud properties from satellite passive radiometer observations are derived by treating a cloud pixel as a single‐layer cloud, resulting in biases in our understanding of clouds and their radiative forcing. This study improves the capabilities of passive radiometers for retrieving properties of ice‐over‐water clouds, including the optical thicknesses and effective radii of both upper ice and lower liquid water clouds simultaneously. Our method provides a new perspective for radiometer‐based retrieval of multilayer cloud properties and will improve the evaluation of cloud radiative effects. Key Points: A cloud microphysical and optical property retrieval algorithm for ice‐over‐water clouds using passive satellite observations is developedThe absorptivity differences of water and ice at three shortwave‐infrared channels are used to differentiate between water and ice cloudsThe retrieved cloud optical properties are found to be significantly improved, compared to MODIS‐derived properties [ABSTRACT FROM AUTHOR]