Detecting the ratio of rain and cloud water in low-latitude shallow marine clouds

Satellite observations are used to deduce the relationship between cloud water attenuation and total water attenuation for low-latitude shallow marine clouds. The specific sensors that facilitate the analysis are the co-located CloudSat profiling radar and the MODerate resolution Imaging Spectroradiometer (MODIS). The separation of the cloud water and precipitation water signals relies on the relative insensitivity of MODIS to the presence of precipitation water in conjunction with observations of the total attenuation of the CloudSat radar beam. The precipitation water attenuation is shown to depend on both the cloud water path and the cloud effective radius suggesting both macrophysical and microphysical controls on the production of precipitation water. The unique combination of total attenuation and cloud attenuation observations are used to place bounds on the mean relationship between the total water path and the cloud water path in shallow marine clouds. This relationship provides a parameterization of the ratio of precipitation water to cloud water, a quantity that is commonly assumed in operational rain rate retrieval algorithms.