Extinction coefficients retrieved in deep tropical ice clouds from lidar observations using a CALIPSO-like algorithm compared to in-situ measurements from the cloud integrating nephelometer during CRYSTAL-FACE

摘要

This paper presents a comparison of lidar ratios and volume extinctioncoefficients in tropical ice clouds, retrieved using observations from twoinstruments: the 532-nm Cloud Physics Lidar (CPL), and the in-situ Cloud Integrating Nephelometer (CIN) probe. Both instrumentswere mounted on airborne platforms during the CRYSTAL-FACE campaign and tookmeasurements up to 17 km. Coincident observations from two cases of iceclouds located on top of deep convective systems are compared. First, lidarratios are retrieved from CPL observations of attenuated backscatter, usinga retrieval algorithm for opaque cloud similar to one used in the recentlylaunched CALIPSO mission, and compared to results from the regular CPLalgorithm. These lidar ratios are used to retrieve extinction coefficientprofiles, which are compared to actual observations from the CIN in-situprobe, putting the emphasis on their vertical variability. When observationscoincide, retrievals from both instruments are very similar, in the limitsof colocation. Differences are generally variations around the averageprofiles, and general trends on larger spatial scales are well reproduced.The two instruments agree well, with an average difference of less than11% on optical depth retrievals. Results suggest the CALIPSO DeepConvection algorithm can be trusted to deliver realistic estimates of thelidar ratio, leading to good retrievals of extinction coefficients.